Triangle Count

Given an array of integers, how many three numbers can be found in the array, so that we can build an triangle whose three edges length is the three numbers that we find?

Have you met this question in a real interview? 

Yes

Example

Given array S = [3,4,6,7], return 3. They are:

[3,4,6]
[3,6,7]
[4,6,7]

Given array S = [4,4,4,4], return 4. They are:

[4(1),4(2),4(3)]
[4(1),4(2),4(4)]
[4(1),4(3),4(4)]
[4(2),4(3),4(4)]

public class Solution {
    /**
     * @param S: A list of integers
     * @return: An integer
     */
    public int triangleCount(int S[]) {
        // write your code here
        
        Arrays.sort(S);
        
        int count = 0;
        for(int i =  S.length - 1; i >= 0; i--){
            int left = 0, right = i - 1;
            
            while(left < right){
                if(S[left] + S[right] <= S[i]){
                    left++;
                } else {
                    count += right - left;
                    right--;
                }
            }
        }
        return count;
        
    }
}