0015. 3Sum

1015. 3Sum

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array 
which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-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>& nums) {
        sort(nums.begin(), nums.end());
        vector<vector<int> > ans;
        vector<int> tmp;
        int size = nums.size(), i;
        for(i=0; i<size-2; i++){
            if(i && nums[i] == nums[i-1]) continue;
            int l = i + 1, r = size - 1, sum = -nums[i];
            while(l < r){
                if(nums[l] + nums[r] < sum)
                    l++;
                else if(nums[l] + nums[r] > sum)
                    r--;
                else{
                    tmp.push_back(nums[i]);
                    tmp.push_back(nums[l]);
                    tmp.push_back(nums[r]);
                    ans.push_back(tmp);
                    tmp.clear();
                    l++, r--;
                    while(nums[l] == nums[l-1]) l++;
                    while(nums[r] == nums[r+1]) r--;
                }
            }
        }
        return ans;
        
    }
};