leetcode:三数之和

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) 
    {
        vector<vector<int>> ret;
        sort(nums.begin(),nums.end());
        int i=0;
        while(i<nums.size())
        {
            while(i>0&&i<nums.size()&&nums[i]==nums[i-1])
            {
                i++;     
            }
            int left = i+1;
            int right = nums.size()-1;
            while(left<right)
            {
                int sum = nums[i]+nums[left]+nums[right];
                if(sum<0)
                {
                    left++;
                }
                else if(sum>0)
                {
                    right--;
                }
                else
                {
                    ret.push_back({nums[i],nums[left],nums[right]});
                    left++;
                    right--;
                    while(left<right&&nums[left]==nums[left-1])
                    {
                        left++;
                    }
                    while(left<right&&nums[right]==nums[right+1])
                    {
                        right--;
                    }
                }
            }
            i++;
        }
        return ret;
    }
};