【一天一道LeetCode】#18. 4Sum

一天一道LeetCode

（一）题目

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)

（二）解题

class Solution {
public:
vector<vector<int>> fourSum(vector<int>& nums, int target) {
vector<vector<int>> result;
if(nums.size()<4) return result;
sort(nums.begin(),nums.end());
for(int i = 0 ; i < nums.size()-3 ; )
{
for(int j=i+1 ; j < nums.size()-2 ; )
{
int start = j+1;
int end = nums.size()-1;
while(start<end)
{
int sum = nums[i]+nums[j]+nums[start]+nums[end];
if(sum==target)
{
vector<int> vec;
vec.push_back(nums[i]);
vec.push_back(nums[j]);
vec.push_back(nums[start]);
vec.push_back(nums[end]);
result.push_back(vec);
start++;
while(start<end && nums[start] == nums[start-1]) start++;
end--;
while(start<end && nums[end] == nums[end+1]) end--;
}
else if(sum>target)
{
end--;
while(start<end && nums[end] == nums[end+1]) end--;
}
else {
start++;
while(start<end && nums[start] == nums[start-1]) start++;;
}
}
j++;
while(j<nums.size()-2 && nums[j] == nums[j-1]) j++;
}
i++;
while(i<nums.size()-3 && nums[i] == nums[i-1]) i++;
}
return result;
}
};