Counting Triangles

You are given an array of N non-negative integers, A0, A1 ,…, AN-1.
Considering each array element Ai as the edge length of some line segment, count the number of triangles which you can form using these array values.

Notes:

  1. You can use any value only once while forming each triangle. Order of choosing the edge lengths doesn’t matter. Any triangle formed should have a positive area.

  2. Return answer modulo 109 + 7.

For example,

A = [1, 1, 1, 2, 2]

Return: 4
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