Leetcode题解 - 15. 3Sum

题目原文：

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: 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]
]

我的答案：Runtime: 69 ms, Your runtime beats 21.06% of cpp submissions

class Solution {public:    vector<vector<int>> threeSum(vector<int>& nums) {        vector<vector<int>> r;        // sort first        sort(nums.begin(), nums.end());        // search        for(int i=0; i<nums.size(); i++){            if( i>0 && (nums[i] == nums[i-1]) ) continue;            for(int j=i+1; j<nums.size(); j++){                if( j>i+1 && nums[j] == nums[j-1] ) continue;                for(int k=j+1; k<nums.size(); k++){                    if( k>j+1 && nums[k] == nums[k-1] ) continue;                    if( nums[i] + nums[j] + nums[k] == 0 ) {                        vector<int> a = {nums[i], nums[j], nums[k]};                        r.push_back(a);                    }                }            }        }        return r;    }};