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3Sum Smaller

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Description

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.

Example:

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Input: nums = [-2,0,1,3], and target = 2
Output: 2 
Explanation: Because there are two triplets which sums are less than 2:
             [-2,0,1]
             [-2,0,3]

Solution

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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 left = i + 1;
            int right = nums.size() - 1;
            while(left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if(sum >= target) {
                    --right;
                }else {
                    count += (right - left);
                    ++left;
                    
                }
                
            }
            
        }
        return count;
    }
};