三个数相加和为零(3Sum)

15. 3Sum

Medium

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Given an array ​​nums​​ of n integers, are there elements a, b, c in ​​nums​​ such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        vector<vector<int> > Result;
        if(nums.size() <= 2){return Result;}
        sort(nums.begin(),nums.end());
        for(int k = 0;k < nums.size();k++){
            if(k > 0 && nums[k] == nums[k - 1]){continue;}
            if(nums[k] > 0){return Result;}
            int target = 0 - nums[k];
            int LeftIndex = k + 1;int RightIndex = nums.size() - 1;
            while(LeftIndex < RightIndex){
                if(target == nums[LeftIndex] + nums[RightIndex]){
                    Result.push_back({nums[k],nums[LeftIndex],nums[RightIndex]});
                    while(LeftIndex < RightIndex && nums[LeftIndex] == nums[LeftIndex + 1]){
                        LeftIndex++;
                    }
                    while(RightIndex > LeftIndex && nums[RightIndex] == nums[RightIndex - 1]){
                        RightIndex--;
                    }
                    LeftIndex += 1;
                    RightIndex -= 1;
                }
                else if(target < nums[LeftIndex] + nums[RightIndex]){
                    RightIndex--;
                }
                else if(target > nums[LeftIndex] + nums[RightIndex]){
                        LeftIndex++;
                    }
                }
            }
            return Result;
    }
};