3Sum Smaller

Given an array of

nintegersnumsand atarget, 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]`

, andtarget= 2.Return 2. Because there are two triplets which sums are less than 2:

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

Follow up:

Could you solve it inO(n^{2}) runtime?

//Sort it , and then use two pointers algorithm class Solution { public: int threeSumSmaller(vector<int>& nums, int target) { if(nums.size() < 3) return 0; sort(nums.begin(), nums.end()); int count = 0; for(int i = 0; i < nums.size() - 2; i++){ int j = i + 1; int k = nums.size() - 1; while(j < k){ int sum = nums[i] + nums[j] + nums[k]; if(sum < target){ count += k - j; j++; } else{ k--; } } } return count; } };