LeetCode·15. 3Sum

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题目：

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]
]

思路：

2-sum问题基础上加一层循环

代码：

class Solution {
public:vector<vector<int>> threeSum(vector<int>& nums) {vector<vector<int>> vec;if(nums.size() == 0)return vec;sort(nums.begin(), nums.end());vector<int> v(3);int sum = 0;for(int i = 0; i < nums.size()-2; ++i){if(nums[i] > 0) return vec;sum = 0 - nums[i];v[0] = nums[i];for(int j = i+1, k = nums.size()-1; j <= k-1;){if(nums[j]+nums[k] == sum){v[1] = nums[j];v[2] = nums[k];vec.push_back(v);if(nums[j] != nums[k]){while((j < k) && nums[++j] == nums[j-1]){}while((j < k) && nums[--k] == nums[k+1]){}}else{break;}}else if(nums[j]+nums[k] < sum){++j;}else if(nums[j]+nums[k] > sum){--k;}}while(i < nums.size()-2 && nums[i+1] == nums[i])++i;}return vec;}
};

结果：

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