3Sum Smaller

Problem:

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.

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]

Analysis:
题意又理解错了，人家并没有要求去重复。If found current sum < target, then from l to r all sums are smaller than target. Similar to Valid Triangle Number.

Solution:

class Solution {
    public int threeSumSmaller(int[] nums, int target) {
        int res = 0;
        if (nums == null || nums.length == 0) return res;
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            int l = i + 1, r = nums.length - 1;
            while (l < r) {
                int sum = nums[l] + nums[r] + nums[i];
                if (sum < target) {
                    res += (r - l);
                    l++;
                } else {
                    r--;
                }
            }
        }

        return res;
    }
}