LeetCode 15 3Sum

15. 3Sum

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Total Accepted: 111041  Total Submissions: 595068  Difficulty: Medium

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)

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在一个数组里找三个数，让其相加等于0

第一次裸O(n^3)暴力，妥妥超时了。

稍稍优化了一下，就能过了。

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums)
    {
        vector<vector<int>> ret;
        sort(nums.begin(),nums.end());
        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> temp;
                                        temp.push_back(nums[i]);
                                        temp.push_back(nums[j]);
                                        temp.push_back(nums[k]);
                                        ret.push_back(temp);
                                }
                        }
                }
        }
        return ret;
    }
};