Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
The solution set must not contain duplicate quadruplets.
Example:
Given array nums = [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] ]
采用与15题相同的思路，只不过，这里是先确定两个数，然后用双指针法。
class Solution {
public:
vector<vector<int>> fourSum(vector<int>& nums, int target) {
vector<vector<int>>result;
sort(nums.begin(),nums.end());
for(int i=0;i<nums.size();i++){
for(int j=i+1;j<nums.size();j++){
int low=j+1,high=nums.size()-1;
int tempsum=-nums[i]-nums[j]+target;
while(low<high){
if(nums[low]+nums[high]==tempsum){
vector<int>temp;
temp.push_back(nums[i]);temp.push_back(nums[j]);
temp.push_back(nums[low]);temp.push_back(nums[high]);
result.push_back(temp);
while(low<high&&nums[low+1]==nums[low])
low++;
low++;
while(low<high&&nums[high]==nums[high-1])
high--;
high--;
}
else if(nums[low]+nums[high]<tempsum)
low++;
else
high--;
}
while(j<nums.size()-1&&nums[j]==nums[j+1])
j++;
}
while(i<nums.size()-1&&nums[i]==nums[i+1])
i++;
}
return result;
}
};