<p>Given an integer array <code>nums</code>, return <em>the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [2,2,3,4]
<strong>Output:</strong> 3
<strong>Explanation:</strong> Valid combinations are: 
2,3,4 (using the first 2)
2,3,4 (using the second 2)
2,2,3
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [4,2,3,4]
<strong>Output:</strong> 4
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 1000</code></li>
	<li><code>0 &lt;= nums[i] &lt;= 1000</code></li>
</ul>

class Solution {
 public:
  int triangleNumber(vector<int>& nums) {
    if (nums.size() < 3)
      return 0;

    int ans = 0;

    ranges::sort(nums);

    for (int k = nums.size() - 1; k > 1; --k) {
      int i = 0;
      int j = k - 1;
      while (i < j)
        if (nums[i] + nums[j] > nums[k]) {
          ans += j - i;
          --j;
        } else {
          ++i;
        }
    }

    return ans;
  }
};
15600