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

public class Solution {
    public int nTriang(int[] arr) {
        int MOD = 1_000_000_007;
        Arrays.sort(arr);
        int n = arr.length;
        long count = 0;
        for (int i = n - 1; i >= 1; --i) {
            int j = 0;
            int k = i - 1;
            while (j < k) {
                if (arr[j] + arr[k] > arr[i]) {
                    count = (count + k - j) % MOD;
                    k--;
                } else
                    j++;
            }
        }
        return (int) count;
    }
}