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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="unordered.comparison"></a><a class="link" href="comparison.html" title="Comparison with Associative Containers">Comparison with Associative Containers</a>
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</h2></div></div></div>
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<div class="table">
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<a name="unordered.comparison.interface_differences"></a><p class="title"><b>Table 45.4. Interface differences.</b></p>
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<div class="table-contents"><table class="table" summary="Interface differences.">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Associative Containers
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</p>
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</th>
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<th>
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<p>
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Unordered Associative Containers
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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Parameterized by an ordering relation <code class="computeroutput"><span class="identifier">Compare</span></code>
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</p>
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</td>
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<td>
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<p>
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Parameterized by a function object <code class="computeroutput"><span class="identifier">Hash</span></code>
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and an equivalence relation <code class="computeroutput"><span class="identifier">Pred</span></code>
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Keys can be compared using <code class="computeroutput"><span class="identifier">key_compare</span></code>
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which is accessed by member function <code class="computeroutput"><span class="identifier">key_comp</span><span class="special">()</span></code>, values can be compared using
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<code class="computeroutput"><span class="identifier">value_compare</span></code> which
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is accessed by member function <code class="computeroutput"><span class="identifier">value_comp</span><span class="special">()</span></code>.
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</p>
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</td>
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<td>
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<p>
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Keys can be hashed using <code class="computeroutput"><span class="identifier">hasher</span></code>
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which is accessed by member function <code class="computeroutput"><span class="identifier">hash_function</span><span class="special">()</span></code>, and checked for equality using
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<code class="computeroutput"><span class="identifier">key_equal</span></code> which is
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accessed by member function <code class="computeroutput"><span class="identifier">key_eq</span><span class="special">()</span></code>. There is no function object for
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compared or hashing values.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Constructors have optional extra parameters for the comparison object.
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</p>
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</td>
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<td>
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<p>
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Constructors have optional extra parameters for the initial minimum
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number of buckets, a hash function and an equality object.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Keys <code class="computeroutput"><span class="identifier">k1</span></code>, <code class="computeroutput"><span class="identifier">k2</span></code> are considered equivalent if
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<code class="computeroutput"><span class="special">!</span><span class="identifier">Compare</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span> <span class="identifier">k2</span><span class="special">)</span> <span class="special">&&</span>
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<span class="special">!</span><span class="identifier">Compare</span><span class="special">(</span><span class="identifier">k2</span><span class="special">,</span> <span class="identifier">k1</span><span class="special">)</span></code>
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</p>
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</td>
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<td>
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<p>
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Keys <code class="computeroutput"><span class="identifier">k1</span></code>, <code class="computeroutput"><span class="identifier">k2</span></code> are considered equivalent if
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<code class="computeroutput"><span class="identifier">Pred</span><span class="special">(</span><span class="identifier">k1</span><span class="special">,</span> <span class="identifier">k2</span><span class="special">)</span></code>
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Member function <code class="computeroutput"><span class="identifier">lower_bound</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code> and <code class="computeroutput"><span class="identifier">upper_bound</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>
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</p>
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</td>
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<td>
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<p>
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No equivalent. Since the elements aren't ordered <code class="computeroutput"><span class="identifier">lower_bound</span></code>
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and <code class="computeroutput"><span class="identifier">upper_bound</span></code> would
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be meaningless.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>
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returns an empty range at the position that k would be inserted if
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k isn't present in the container.
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</p>
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</td>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>
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returns a range at the end of the container if k isn't present in
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the container. It can't return a positioned range as k could be inserted
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into multiple place. To find out the bucket that k would be inserted
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into use <code class="computeroutput"><span class="identifier">bucket</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>.
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But remember that an insert can cause the container to rehash - meaning
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that the element can be inserted into a different bucket.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">iterator</span></code>, <code class="computeroutput"><span class="identifier">const_iterator</span></code> are of the bidirectional
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category.
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</p>
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</td>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">iterator</span></code>, <code class="computeroutput"><span class="identifier">const_iterator</span></code> are of at least
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the forward category.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Iterators, pointers and references to the container's elements are
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never invalidated.
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</p>
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</td>
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<td>
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<p>
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<a class="link" href="buckets.html#unordered.buckets.iterator_invalidation">Iterators
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can be invalidated by calls to insert or rehash</a>. Pointers
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and references to the container's elements are never invalidated.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Iterators iterate through the container in the order defined by the
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comparison object.
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</p>
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</td>
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<td>
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<p>
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Iterators iterate through the container in an arbitrary order, that
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can change as elements are inserted, although equivalent elements
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are always adjacent.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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No equivalent
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</p>
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</td>
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<td>
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<p>
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Local iterators can be used to iterate through individual buckets.
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(The order of local iterators and iterators aren't required to have
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any correspondence.)
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Can be compared using the <code class="computeroutput"><span class="special">==</span></code>,
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<code class="computeroutput"><span class="special">!=</span></code>, <code class="computeroutput"><span class="special"><</span></code>,
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<code class="computeroutput"><span class="special"><=</span></code>, <code class="computeroutput"><span class="special">></span></code>, <code class="computeroutput"><span class="special">>=</span></code>
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operators.
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</p>
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</td>
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<td>
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<p>
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Can be compared using the <code class="computeroutput"><span class="special">==</span></code>
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and <code class="computeroutput"><span class="special">!=</span></code> operators.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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</td>
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<td>
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<p>
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When inserting with a hint, implementations are permitted to ignore
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the hint.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">erase</span></code> never throws
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an exception
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</p>
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</td>
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<td>
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<p>
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The containers' hash or predicate function can throw exceptions from
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<code class="computeroutput"><span class="identifier">erase</span></code>
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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</div>
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<br class="table-break"><div class="table">
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<a name="unordered.comparison.complexity_guarantees"></a><p class="title"><b>Table 45.5. Complexity Guarantees</b></p>
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<div class="table-contents"><table class="table" summary="Complexity Guarantees">
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<colgroup>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Operation
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</p>
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</th>
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<th>
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<p>
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Associative Containers
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</p>
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</th>
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<th>
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<p>
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Unordered Associative Containers
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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Construction of empty container
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</p>
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</td>
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<td>
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<p>
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constant
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</p>
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</td>
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<td>
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<p>
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O(<span class="emphasis"><em>n</em></span>) where <span class="emphasis"><em>n</em></span> is the minimum
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number of buckets.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Construction of container from a range of <span class="emphasis"><em>N</em></span>
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elements
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</p>
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</td>
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<td>
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<p>
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O(<span class="emphasis"><em>N</em></span> log <span class="emphasis"><em>N</em></span>), O(<span class="emphasis"><em>N</em></span>)
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if the range is sorted with <code class="computeroutput"><span class="identifier">value_comp</span><span class="special">()</span></code>
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</p>
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</td>
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<td>
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<p>
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Average case O(<span class="emphasis"><em>N</em></span>), worst case O(<span class="emphasis"><em>N</em></span><sup>2</sup>)
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Insert a single element
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</p>
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</td>
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<td>
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<p>
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logarithmic
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</p>
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</td>
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<td>
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<p>
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Average case constant, worst case linear
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Insert a single element with a hint
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</p>
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</td>
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<td>
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<p>
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Amortized constant if t elements inserted right after hint, logarithmic
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otherwise
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</p>
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</td>
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<td>
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<p>
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Average case constant, worst case linear (ie. the same as a normal
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insert).
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Inserting a range of <span class="emphasis"><em>N</em></span> elements
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</p>
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</td>
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<td>
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<p>
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<span class="emphasis"><em>N</em></span> log(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>+<span class="emphasis"><em>N</em></span>)
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</p>
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</td>
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<td>
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<p>
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Average case O(<span class="emphasis"><em>N</em></span>), worst case O(<span class="emphasis"><em>N</em></span>
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* <code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Erase by key, <code class="computeroutput"><span class="identifier">k</span></code>
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</p>
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</td>
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<td>
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<p>
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O(log(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
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+ <code class="computeroutput"><span class="identifier">count</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>)
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</p>
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</td>
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<td>
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<p>
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Average case: O(<code class="computeroutput"><span class="identifier">count</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>), Worst case: O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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Erase a single element by iterator
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</p>
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</td>
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<td>
|
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<p>
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Amortized constant
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</p>
|
||
</td>
|
||
<td>
|
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<p>
|
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Average case: O(1), Worst case: O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
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</p>
|
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</td>
|
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</tr>
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<tr>
|
||
<td>
|
||
<p>
|
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Erase a range of <span class="emphasis"><em>N</em></span> elements
|
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</p>
|
||
</td>
|
||
<td>
|
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<p>
|
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O(log(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
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+ <span class="emphasis"><em>N</em></span>)
|
||
</p>
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||
</td>
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||
<td>
|
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<p>
|
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Average case: O(<span class="emphasis"><em>N</em></span>), Worst case: O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
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</p>
|
||
</td>
|
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</tr>
|
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<tr>
|
||
<td>
|
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<p>
|
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Clearing the container
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</p>
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||
</td>
|
||
<td>
|
||
<p>
|
||
O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
Find
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||
</p>
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||
</td>
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||
<td>
|
||
<p>
|
||
logarithmic
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
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Average case: O(1), Worst case: O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
Count
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||
</p>
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||
</td>
|
||
<td>
|
||
<p>
|
||
O(log(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
||
+ <code class="computeroutput"><span class="identifier">count</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>)
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
Average case: O(1), Worst case: O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
<code class="computeroutput"><span class="identifier">equal_range</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
logarithmic
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
Average case: O(<code class="computeroutput"><span class="identifier">count</span><span class="special">(</span><span class="identifier">k</span><span class="special">)</span></code>), Worst case: O(<code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>)
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
<tr>
|
||
<td>
|
||
<p>
|
||
<code class="computeroutput"><span class="identifier">lower_bound</span></code>,<code class="computeroutput"><span class="identifier">upper_bound</span></code>
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
logarithmic
|
||
</p>
|
||
</td>
|
||
<td>
|
||
<p>
|
||
n/a
|
||
</p>
|
||
</td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
</div>
|
||
<br class="table-break">
|
||
</div>
|
||
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
|
||
<td align="left"></td>
|
||
<td align="right"><div class="copyright-footer">Copyright © 2003, 2004 Jeremy B. Maitin-Shepard<br>Copyright © 2005-2008 Daniel
|
||
James<p>
|
||
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
||
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||
</p>
|
||
</div></td>
|
||
</tr></table>
|
||
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