15. 3Sum

15. 3Sum

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vector<vector<int>> res;
        if(nums.empty())	return res;
        int n=nums.size();
        std::sort(nums.begin(),nums.end());
        
        for(int i=0;i<n-2;i++){
        	int target=-nums[i],front=i+1,back=n-1;
        	while(front<back){
        		int sum=nums[front]+nums[back];
        		if(sum<target)
        			front++;
        		else if(sum>target)
        			back--;
        		else{
        			vector<int> temp(3,0);
        			temp[0]=nums[i];
        			temp[1]=nums[front];
        			temp[2]=nums[back];
        			res.push_back(temp);
        			while(front<back&&nums[front]==temp[1])
        				front++;
        			while(front<back&&nums[back]==temp[2])
        				back--;
        		}
        	}
        	while(i+1<n&&nums[i+1]==nums[i])
        		i++;
        }

        return res;
    }
};