count the number of possible triangles

1#include<bits/stdc++.h>
2using namespace std;
3
4int count_triangles(int arr[], int n)
5{
6  int ans = 0;
7  for (int i = n - 1; i >= 2; i--){
8    int l = 0, r = i - 1;
9    while(l < r){
10      if (arr[l] + arr[r] > arr[i]){
11        ans += r - l;
12        r--;
13      }
14      else l++;
15  }
16  
17  return ans;
18}