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题目描述：4Sum
Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
For example, given array S = {1 0 -1 0 -2 2}, and target = 0.
A solution set is:
(-1, 0, 0, 1)
(-2, -1, 1, 2)
(-2, 0, 0, 2)
代码如下：
class Solution { public: vector<vector<int> > fourSum(vector<int> &num, int target) { // Note: The Solution object is instantiated only once. vector<vector<int>> res; int numlen = num.size(); if(num.size()<4) return res; sort(num.begin(),num.end()); set<vector<int>> tmpres; for(int i = 0; i < numlen; i++){ for(int j = i + 1; j < numlen; j++){ int begin = j+1; int end = numlen-1; while(begin < end){ int sum = num[i]+ num[j] + num[begin] + num[end]; if(sum == target){ vector<int> tmp; tmp.push_back(num[i]); tmp.push_back(num[j]); tmp.push_back(num[begin]); tmp.push_back(num[end]); tmpres.insert(tmp); begin++; end--; } else if(sum<target) begin++; else end--; } } } set<vector<int>>::iterator it = tmpres.begin(); for(; it != tmpres.end(); it++) res.push_back(*it); return res; } };
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原文地址：http://www.cnblogs.com/510602159-Yano/p/4278894.html
