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18.cpp
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18.cpp
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#include "head.h"
class Solution {
public:
vector<vector<int>> fourSum(vector<int>& nums, int target) {
vector<vector<int>> ans;
if (nums.size()==0)
return ans;
sort(nums.begin(), nums.end());
for (int i=3; i<nums.size(); ++i) {
vector<vector<int>> triplet = threeSum(nums, i, target-nums[i]);
for (int j=0; j<triplet.size(); ++j) {
triplet[j].push_back(nums[i]);
if (!haveExisted(triplet[j], ans))
ans.push_back(triplet[j]);
}
}
return ans;
}
vector<vector<int>> threeSum(vector<int>& nums, int end, int target) {
vector<vector<int>> ans;
for (int i=2; i<end; ++i) {
vector<vector<int>> pairs = twoSum(nums, i, target-nums[i]);
for (int j=0; j<pairs.size(); ++j) {
pairs[j].push_back(nums[i]);
if (!haveExisted(pairs[j], ans))
ans.push_back(pairs[j]);
}
}
return ans;
}
vector<vector<int>> twoSum(vector<int>& nums, int end, int target) {
vector<vector<int>> ans;
int left = 0, right = end-1;
while (left<right) {
while (left<right && nums[left]+nums[right]<target)
++left;
while (left<right && nums[left]+nums[right]>target)
--right;
if (left<right && nums[left]+nums[right]==target) {
vector<int> temp{nums[left], nums[right]};
if (!haveExisted(temp, ans))
ans.push_back(temp);
++left;
--right;
}
}
return ans;
}
bool haveExisted(vector<int>& candidate, vector<vector<int>>& ans) {
for (int i=0; i<ans.size(); ++i) {
bool isEqual = true;
for (int j=0; j<candidate.size(); ++j)
if (candidate[j]!=ans[i][j]) {
isEqual = false;
break;
}
if (isEqual)
return true;
}
return false;
}
};