【leetcode题解】三数之和图解

给你一个包含 n 个整数的数组 nums，判断 nums 中是否存在三个元素 a，b，c ，使得 a + b + c = 0 ？请你找出所有满足条件且不重复的三元组。
注意：答案中不可以包含重复的三元组。

解题思路

代码

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        set<vector<int>> S;
        vector<vector<int>> res;
        int N = nums.size();
        for(int i = 0 ; i < N-2 ; i++)
        {
            if(nums[i] > 0) break;
            if(i > 0 && nums[i] == nums[i-1]) continue;
            int target = -nums[i];
            int leftGuard = i+1;
            int rightGuard = N-1;
            while(leftGuard < rightGuard)
            {
                if(target == nums[leftGuard] + nums[rightGuard])
                {
                    S.insert({nums[i], nums[leftGuard], nums[rightGuard]});
                    while(leftGuard < rightGuard && nums[leftGuard] == nums[leftGuard+1]) leftGuard++;
                    while(leftGuard < rightGuard && nums[rightGuard] == nums[rightGuard-1]) rightGuard--;
                    leftGuard++;
                    rightGuard--;
                }
                else if(nums[leftGuard] + nums[rightGuard] > target) rightGuard--;
                else leftGuard++;
            }
        }
        for(auto it : S)
        {
            res.push_back(it);
        }
        return res;
    }
};