Leetcode 15. 3Sum

15. 3Sum

• Total Accepted: 130571
• Total Submissions: 670539
• Difficulty: Medium

Given an array S of n integers, are there elements a, b, c in S 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.

For example, given array S = [-1, 0, 1, 2, -1, -4],

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

思路：基本思路和Leetcode 16. 3Sum Closest类似，但要注意去除集合元素完全相同的集合，就是去除相同集合。

代码：

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        vector<vector<int>> res;
        int i,j,k,n=nums.size(),temp;
        for(i=0;i<n;i++){
            j=i+1;
            k=n-1;
            while(j<k){
                int ans=nums[i]+nums[j]+nums[k];
                if(ans==0){
                    res.push_back({nums[i],nums[j],nums[k]});
                    while(j<k&&nums[j]==nums[j+1]) j++;
                    while(k>j&&nums[k]==nums[k-1]) k--;
                }
                if(ans>=0) k--;
                if(ans<=0) j++;
            }
            while(i+1<n&&nums[i]==nums[i+1]) i++;
        }
        return res;
    }
};