3Sum

最新推荐文章于 2018-10-17 20:00:26 发布

撄宁之境

最新推荐文章于 2018-10-17 20:00:26 发布

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分类专栏： LeetCode 文章标签： LeetCode 算法

本文链接：https://blog.youkuaiyun.com/huangynn/article/details/38715725

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探讨了如何在整数数组中寻找三个数使它们的和等于零的问题，并提供了一个有效的算法解决方案。该算法首先对数组进行排序，然后通过双指针技术遍历数组来寻找所有不重复的三元组。

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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)

排序后固定一个数i，i当num[j]+num[k]+num[i]<0的时候j++ 两边夹逼

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