vector<vector<int>> fourSum(vector<int>& nums, int target) {
vector<vector<int>> res;
if (nums.empty()) return res;
std::sort(nums.begin(),nums.end());
for (int i = 0; i < nums.size(); i++) {
int target3 = target - nums[i];
for (int j = i+1; j < nums.size(); j++) {
int target2 = target3 - nums[j];
int l = j+1, r = nums.size()-1;
while ( l < r) {
if (target2 > (nums[l]+nums[r]) ) l++;
else if (target2 < (nums[l]+nums[r]) ) r--;
else {
vector<int> quadruplet(4, 0);
quadruplet[0] = nums[i];
quadruplet[1] = nums[j];
quadruplet[2] = nums[l];
quadruplet[3] = nums[r];
res.push_back(quadruplet);
while (l < r && nums[l] == quadruplet[2]) l++;
while (l < r && nums[r] == quadruplet[3]) r--;
}
}
while(j + 1 < nums.size() && nums[j + 1] == nums[j]) j++;
}
while (i + 1 < nums.size() && nums[i + 1] == nums[i]) i++;
}
return res;
}
vector<vector<int> > fourSum(vector<int> &num, int target) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
int len = num.size();
vector<vector<int>> result;
if(len<4)
return result;
sort(num.begin(),num.end());
for(int i=0;i<len;i++)
{
if(i>0 && num[i]==num[i-1]) continue; // avoid duplicates
for(int j=i+1;j<len;j++)
{
if(j>i+1 && num[j]==num[j-1]) continue; // avoid duplicates
int TwoSum = num[i] + num[j];
int SumLeft = target - TwoSum;
int m = j+1;
int n = len-1;
while(m<n)
{
int sum = num[m]+num[n];
if(sum == SumLeft)
{
vector<int> quadruplet(4);
quadruplet[0] = num[i];
quadruplet[1] = num[j];
quadruplet[2] = num[m];
quadruplet[3] = num[n];
result.push_back(quadruplet);
while(m<n && num[m+1]==num[m]) m++; // avoid duplicates
while(m<n && num[n-1]==num[n]) n--; // avoid duplicates
m++; // dont forget to increment m
n--;
}
else if(sum<SumLeft)
m++;
else
n--;
}
}
}
return result;
}
vector<vector<int>> fourSum(vector<int>& nums, int target) {
vector<vector<int>> res;
if (nums.size() < 4) return res;
sort(nums.begin(), nums.end());
int cur1 = nums[0];
vector<int> quadruplet(4, 0);
for (int i = 0; i < nums.size() - 3; i ++)
{
if (cur1 == nums[i] && i != 0) continue;
int cur2 = nums[i+1];
for (int j = i+1; j < nums.size() - 2; j ++)
{
if (cur2 == nums[j] && j != i+1) continue;
int m = j + 1, n = nums.size() - 1;
while (m < n)
{
if (nums[m] + nums[n] + nums[i] + nums[j] == target)
{
quadruplet[0] = nums[i];
quadruplet[1] = nums[j];
quadruplet[2] = nums[m];
quadruplet[3] = nums[n];
res.push_back(quadruplet);
m ++;
n --;
}
else if (nums[m] + nums[n] + nums[i] + nums[j] < target) m ++;
else n --;
}
cur2 = nums[j];
}
cur1 = nums[i];
}
// avoid repeating
auto it = unique(res.begin(), res.end());
res.resize(distance(res.begin(), it));
return res;
}
