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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)
1 class Solution { 2 public: 3 vector<vector<int> > fourSum(vector<int> &num, int target) { 4 5 int n=num.size(); 6 int i,j,k,l; 7 int a,b,c,d; 8 sort(num.begin(),num.end()); 9 vector<vector<int> > result; 10 for(int i=0;i<n-3;i++) 11 { 12 for(int j=i+1;j<n-2;j++) 13 { 14 k=j+1; 15 l=n-1; 16 17 while(k<l) 18 { 19 a=num[i]; 20 if(i>0&&num[i]==num[i-1]) 21 { 22 break; 23 } 24 25 b=num[j]; 26 if(j>i+1&&num[j]==num[j-1]) 27 { 28 break; 29 } 30 31 c=num[k]; 32 if(k>j+1&&num[k]==num[k-1]) 33 { 34 k++; 35 continue; 36 } 37 38 d=num[l]; 39 if(l<n-1&&num[l]==num[l+1]) 40 { 41 l--; 42 continue; 43 } 44 45 int sum=a+b+c+d; 46 47 if(sum<target) 48 { 49 k++; 50 } 51 else if(sum>target) 52 { 53 l--; 54 } 55 else 56 { 57 vector<int> tmp(4); 58 tmp[0]=a; 59 tmp[1]=b; 60 tmp[2]=c; 61 tmp[3]=d; 62 result.push_back(tmp); 63 k++; 64 l--; 65 } 66 } 67 } 68 } 69 return result; 70 } 71 };
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原文地址：http://www.cnblogs.com/reachteam/p/4190367.html
