valid-triangle-number.md

Given an array consists of non-negative integers,  your task is to count the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle.

<p><b>Example 1:</b><br />
<pre>
<b>Input:</b> [2,2,3,4]
<b>Output:</b> 3
<b>Explanation:</b>
Valid combinations are: 
2,3,4 (using the first 2)
2,3,4 (using the second 2)
2,2,3
</pre>
</p>

<p><b>Note:</b><br>
<ol>
<li>The length of the given array won't exceed 1000.</li>
<li>The integers in the given array are in the range of [0, 1000].</li>
</ol>
</p>