[算法练习]3 三数之和

例如, 给定数组 nums = [-1, 0, 1, 2, -1, -4]，
满足要求的三元组集合为：[[-1, 0, 1],[-1, -1, 2]]

class Solution {public:    vector<int> twoSum(vector<int>& nums, int target) {        //int result[]={0.1};        int i=  0;        int j=0;        for(i;i<nums.size()-1;i++)        {            for(j=i+1;j<nums.size();j++)            {                if(nums[i]+nums[j]==target)//numb i + numbs[j] - target = 0                {                    return {i,j};                }            }        }        return {i,j};    }};

class Solution {public:    vector<vector<int>> threeSum(vector<int>& nums) {         int target;        vector<vector<int>> ans;        sort(nums.begin(), nums.end());        for (int i = 0; i < nums.size(); i++) {            if (i > 0 && nums[i] == nums[i - 1]) continue;            if ((target = nums[i]) > 0) break;            int left = i + 1, right = nums.size() - 1;            //取出三个数 所以不用left=right            while (left < right) {                if (nums[left] + nums[right] + target < 0) ++left;                else if (nums[left] + nums[right] + target > 0) --right;                else {                    ans.push_back({target, nums[left], nums[right]});                    ++left, --right;                    //去重                     //测试数据[-2,0,0,2,2]                    while (left < right && nums[left] == nums[left - 1]) ++left;                    while (left < right && nums[right] == nums[right + 1]) --right;                }            }        }        return ans;     }};