3Sum

Code:

class Solution {
public:
    vector<vector<int>> threeSum(vector<int> &num) {
        vector<int> buf;
        vector<vector<int>> res;
        if(num.empty()) return res;
        sort(num.begin(),num.end());
        int n=num.size();
        int i,j,k;
        for(i=0;i<n-2;i++)
        {
            j=i+1;
            k=n-1;
            while(j<k)
            {
                if(num[i]+num[j]+num[k]==0)
                {
                    buf.clear();
                    buf.push_back(num[i]);
                    buf.push_back(num[j]);
                    buf.push_back(num[k]);
                    res.push_back(buf);
                    j++;
                    k--;
                    while(j<k&&num[j-1]==num[j]) j++;
                    while(j<k&&num[k]==num[k+1]) k--;
                }
                else if(num[i]+num[j]+num[k]<0)
                    j++;
                else
                    k--;
            }
            while(i<n-2&&num[i]==num[i+1])
                i++;
        }
        return res;
    }
};