<div>
<blockquote>
the array has series of numbers 
</blockquote>
<br />
if you now have <br />
<br />

<pre><code id="code-20-42172864-1">std::vector&lt; std::vector&lt;int&gt; &gt; series; </code></pre>
<br />
where some of the series elements are arrays with size 2, you could create a second array only containing pointers to pairs like <br />
<br />

<pre><code id="code-20-42172864-2">std::vector&lt; std::vector&lt;int, int&gt; * &gt; pairs;
std::vector&lt; std::vector&lt;int&gt; &gt;::iterator i;
for (i = series.begin(); i != series.end(); ++i)
    if (i-&gt;size() == 2) 
         pairs.push_back(&amp;(*i));</code></pre>
<br />
but since you need to store the pointers it is not O(n).<br />
<br />
Sara
</div>


> the array has series of numbers


if you now have



std::vector< std::vector<int> > series; 


where some of the series elements are arrays with size 2, you could create a second array only containing pointers to pairs like



std::vector< std::vector<int, int> * > pairs;
std::vector< std::vector<int> >::iterator i;
for (i = series.begin(); i != series.end(); ++i)
    if (i->size() == 2) 
         pairs.push_back(&(*i));


but since you need to store the pointers it is not O(n).

Sara

<div>
The question requires the following two items in identifying pairs of numbers that add up to a given SUM:<br />
1) hash table<br />
2) O(n) complexity.<br />
The solution adheres to both of these requirements.
</div>


The question requires the following two items in identifying pairs of numbers that add up to a given SUM:
1) hash table
2) O(n) complexity.
The solution adheres to both of these requirements.

<div>
<div class="content wysiwyg-content">
the array has series of numbers Need to find all pairs in the array using a hash table <br />
integers ...
</div>
</div>


the array has series of numbers Need to find all pairs in the array using a hash table 
integers ...

I need to find all pairs in an array equal to a sum complexity 0(n) right away and in c++

C++ is an intermediate-level general-purpose programming language, not to be confused with C or C#. It was developed as a set of extensions to the C programming language to improve type-safety and add support for automatic resource management, object-orientation, generic programming, and exception handling, among other features.

An algorithm is a self-contained step-by-step set of operations to be performed. Algorithms exist that perform calculation, data processing, and automated reasoning. Starting from an initial state and initial input (perhaps empty), the instructions describe a computation that, when executed, proceeds through a finite number of well-defined successive states, eventually producing "output" and terminating at a final ending state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate random input.