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3Sum.cpp
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3Sum.cpp
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/*
Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0?
Find all unique triplets in the array which gives the sum of zero.
Note:
Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
The solution set must not contain duplicate triplets.
For example, given array S = {-1 0 1 2 -1 -4},
A solution set is:
(-1, 0, 1)
(-1, -1, 2)
*/
class Solution {
public:
vector<vector<int> > threeSum(vector<int> &num) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
sort(num.begin(),num.end());
int len = num.size();
vector<vector<int>> result;
for(int i=0;i<len-2;i++)
{
if(num[i]>0)
break;
if(i>0 && num[i]==num[i-1]) // check the duplicates
continue;
int j =i+1;
int k=len-1;
while(j<k)
{
int sum = num[i]+num[j]+num[k];
if(sum==0)
{
vector<int> curr;
curr.push_back(num[i]);
curr.push_back(num[j]);
curr.push_back(num[k]);
result.push_back(curr);
j++;k--;
while(j<k && num[j]==num[j-1]) j++; //check the duplicates
while(j<k && num[k]==num[k+1]) k--; //check the duplicates
}
else if(sum>0)
k--;
else
j++;
}
}
return result;
}
};