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:

  • Elements in a quadruplet (a,b,c,d) must be in non-descending order. (ie, a ≤ b ≤ c ≤ d)
  • The solution set must not contain duplicate quadruplets.

 

    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     vector<vector<int>> fourSum(vector<int>& nums, int target) {
 2         sort(nums.begin(),nums.end());
 3         int len=nums.size(),i,j;
 4         int sum,sum1,ileft,iright;
 5         vector<vector<int> > res;
 6         for(i=0;i<len-3;i++)
 7         {
 8             if(i > 0 && nums[i] == nums[i-1]) continue;
 9             for(j=i+1;j<len-2;j++)
10             {if(j > i+1 && nums[j] == nums[j-1]) continue;
11             sum=nums[i]+nums[j];
12             ileft=j+1;iright=len-1;
13             while(ileft<iright)
14             {
15                 sum1=nums[ileft]+nums[iright];
16                 if(sum1+sum==target)
17                 {
18                     vector<int> tmp;
19                     tmp.push_back(nums[i]);
20                     tmp.push_back(nums[j]);
21                     tmp.push_back(nums[ileft]);
22                     tmp.push_back(nums[iright]);
23                     res.push_back(tmp);
24                    
25                     while(ileft<iright)
26                     {
27                         if(nums[ileft]==nums[ileft+1])
28                         ileft++;
29                         else
30                         {ileft++;break;}
31                     }
32                     while(ileft<iright)
33                     {
34                         if(nums[iright]==nums[iright-1])
35                         iright--;
36                         else
37                         {iright--;break;}
38                     }
39                     
40                 }
41                 else if(sum1+sum<target)
42                 ileft++;
43                 else
44                 iright--;
45             }
46             }
47             
48             
49             //while(left<right&&nums[left]==nums[left+1])left++;
50             //while(left<right&&nums[right]==nums[right-1])right--;
51             
52         }
53         return res;
54     }