3Sum Smaller.java

/*
    Given an array of n integers nums and a target, find the number of index triplets i, j, k with 0 <= i < j < k < n that 
    satisfy the condition nums[i] + nums[j] + nums[k] < target.
    
    Link: https://leetcode.com/problemset/algorithms/

    Example:  
      	For example, given nums = [-2, 0, 1, 3], and target = 2.
		Return 2. Because there are two triplets which sums are less than 2:

		[-2, 0, 1]
		[-2, 0, 3]

    Solution: None

    Source: https://segmentfault.com/a/1190000003794736
*/

public class Solution {
    public int threeSumSmaller(int[] nums, int target) {
        Arrays.sort(nums);
        int cnt = 0;
        for (int i = 0; i < nums.length - 2; i++){
            int left = i + 1, right = nums.length - 1;
            while (left < right){
                int sum = nums[i] + nums[left] + nums[right];
                if (sum >= target){
                    right--;
                } else {
                    cnt += right - left;
                    left++;
                }
            }
        }
        return cnt;
    }
}