leetcode/15.cpp at main · will-s-h/leetcode · GitHub

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class Solution {
public:

    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(), nums.end()); //O(n log n)

        vector<vector<int>> sols;

        for(int i = 0; i < nums.size(); i++){
            if(i > 0 && nums[i] == nums[i-1]) continue;
            int sum = -nums[i];

            int l = i+1; //left index
            int r = nums.size()-1; //right index

            while(l < r){
                while(l < r && nums[l] + nums[r] > sum){
                    r--;
                }

                if(l < r && nums[l] + nums[r] == sum){
                    sols.push_back({nums[i], nums[l], nums[r]});
                }

                l++;

                while(l < r && nums[l] == nums[l-1]) l++;
            }
        }

        return sols;
    }
};