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| class Solution {
public:
vector<vector<int>> fourSum(vector<int>& nums, int target) {
int size = nums.size();
vector<vector<int>> res;
if (size < 4) return res;
sort(nums.begin(), nums.end());
int s1 = 0;
int e1 = size - 1;
while (s1 < e1 - 2) {
if (nums[s1] + nums[e1-2] + nums[e1-1] + nums[e1] < target) s1++;
else if (nums[s1] + nums[s1+1] + nums[s1+2] + nums[e1] > target) e1--;
else {
int tmp1 = s1;
int tmp2 = e1;
twoSum(s1, s1+1, e1-1, e1, res, nums, target);
tmp2--;
while (s1 < tmp2 - 2) {
while (nums[tmp2] == nums[tmp2+1]) tmp2--;
twoSum(s1, s1+1, tmp2-1, tmp2, res, nums, target);
tmp2--;
}
tmp1++;
while (tmp1 < e1 - 2) {
while (nums[tmp1] == nums[tmp1-1]) tmp1++;
twoSum(tmp1, tmp1+1, e1-1, e1, res, nums, target);
tmp1++;
}
e1--;
while (s1 < e1 - 2 && nums[e1] == nums[e1+1]) e1--;
s1++;
while (s1 < e1 - 2 && nums[s1] == nums[s1-1]) s1++;
}
}
sort(res.begin(),res.end());
return res;
}
void twoSum(int s1, int s2, int e2, int e1, vector<vector<int>>& res, vector<int>& nums, int target) {
while (s2 < e2) {
if (nums[s1] + nums[s2] + nums[e2] + nums[e1] < target) s2++;
else if (nums[s1] + nums[s2] + nums[e2] + nums[e1] > target) e2--;
else {
vector<int> tmp{nums[s1], nums[s2], nums[e2], nums[e1]};
res.push_back(tmp);
while (s2 < e2 - 1 && nums[s2] == nums[s2+1]) s2++;
s2++;
}
}
return;
}
};
|