3Sum

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:

• Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
• 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)

这题做得真是郁闷。。。。

C++实现代码：

#include<iostream>

#include<algorithm>

#include<vector>

using namespace std;



class Solution

{

public:

    vector<vector<int> > threeSum(vector<int> &num)

    {

        if(num.empty())

            return vector<vector<int> >();

        sort(num.begin(),num.end());

        vector<vector<int> > ret;

        int n=num.size();

        int i;

        for(i=0; i<n-2; i++)

        {

            //只保留第一个不重复的，其余的都删了

            if(i>=1&&num[i]==num[i-1])

                continue;

            int target=-num[i];

            int left=i+1;

            int right=n-1;

            vector<int> tmp;

            while(left<right)

            {

                //删除重复元素

                if(right>left&&right<n-1&&num[right+1]==num[right])

                    right--;

                else if(num[left]+num[right]==target)

                {

                    tmp={num[i],num[left],num[right]};

                    ret.push_back(tmp);

                    left++;

                    right--;

                }

                else if(num[left]+num[right]<target)

                    left++;

                else if(num[left]+num[right]>target)

                    right--;

            }

        }

        return ret;

    }

};

int main()

{

    vector<int> vec= {-2,0,1,1,1,1,1,2};

    Solution s;

    vector<vector<int> > result=s.threeSum(vec);

    for(auto a:result)

    {

        for(auto v:a)

            cout<<v<<" ";

        cout<<endl;

    }

    cout<<endl;

}