15. 3Sum

15. 3Sum

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        vector<vector<int>> res;
        int n = nums.size();
        for(int i = 0;i < n;i++){
            while(i && i < n && nums[i] == nums[i-1]) i++;
            int j = i + 1,k = n - 1;
            while(j < k){
                int sum = nums[i] + nums[j] + nums[k];
                if(!sum){
                    vector<int>t = { nums[i],nums[j],nums[k] };
                    res.push_back(t);
                    j++; k--;
                    while(j < k && nums[j] == nums[j-1]) j++;
                    while(k > j && nums[k] == nums[k+1]) k--;
                }
                else if(sum < 0){
                    j++;
                    while(j < k && nums[j] == nums[j-1]) j++;
                }
                else{
                    k--;
                    while(k > j && nums[k] == nums[k+1]) k--;
                }
            }
        }
        return res;
    }
};