3Sum

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)

最主要的是对相同的数据进行处理。

class Solution {
public:
vector<vector<int> > threeSum(vector<int> &num) {
sort(num.begin(),num.end());
vector<vector<int> >result;
vector<int>temp;
int n = num.size();
if(n < 3){
return result;
}
for(int i=0; i<n-2 && num[i]<=0; ++i){
if(i > 0 && num[i]==num[i-1]){
continue;
}
int j= i + 1;
int k= n - 1;

while(j < k)
{
if(j > i + 1 && num[j] == num[j - 1]){
j++;
continue;
}
if(k < n - 1 && num[k] == num[k + 1]){
k--;
continue;
}
int sum = num[i] + num[j] + num[k];
if(sum < 0){
j++;
}
else if(sum > 0){
k--;
}
else if(sum == 0)
{
temp.clear();
temp.push_back(num[i]);
temp.push_back(num[j]);
temp.push_back(num[k]);
result.push_back(temp);
j++;
k--;
}
}
}
return result;
}
};