leetcode[15]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)

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