3Sum

Question:

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)

Solution:

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
    vector< vector<int> > result;
    if(nums.size()<3)
        return result;
    sort(nums.begin(),nums.end());
    const int target=0;
    auto last=nums.end();
    for(auto i=nums.begin();i<last-2;i++)
    {
        auto j=i+1;
        if(i>nums.begin() && *i==*(i-1)) continue;
        auto k=last-1;
        while(j<k)
        {
            if(*i+*j+*k<target)
                {j++;while(*j==*(j-1) && j<k) ++j;}
            else if(*i+*j+*k>target)
                {k--;while(*k==*(k+1) && j<k) --k;}
            else
            {
                vector<int> x;
                x.push_back(*i);
                x.push_back(*j);
                x.push_back(*k);
                result.push_back(x);
                ++j;
                --k;
                while(*j==*(j-1) && *k==*(k+1) && j<k) ++j;
            }
        }
    }
    return result;
    }
};