LeetCode-15-3 Sum

算法描述：

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]
]

解题思路：

重要的点：1排序；2 三个指针去重；3注意细节。

        vector<vector<int>> results;
        sort(nums.begin(),nums.end());
        for(int i=0; i < nums.size(); i++){
            if(i >0 && nums[i] == nums[i-1]) continue;
            int low = i+1;
            int high = nums.size()-1;
            while(low < high){
                if(nums[i] + nums[low] + nums[high] == 0){
                    vector<int> temp = {nums[i], nums[low], nums[high]};
                    results.push_back(temp);
                    while(low < high && nums[low] == nums[low+1]) low++;
                    while(low < high && nums[high] == nums[high-1]) high--;
                    low++;
                    high--;
                } else if(nums[i] + nums[low] + nums[high] < 0){
                    low++;
                } else{
                    high--;  
                } 
            }
        }
        return results;
    }