leetcode-3Sum-15

输入一个数组，任选三个数求和，和为0的所有组合，不能重复，即，-1,0,1这样的三元组只能出现一次。

解法：类似两个数求和的方法，先排序，然后首尾指针法，但这里要求三个数，所以还是得遍历一遍，因此第一个数遍历，剩下两个数用首尾指针法，ON^2

对于重复三元组的处理：本来想把所有结果先放入set<node> 里，然后在复制到vector<vector<int> >中返回，但不知道为何不能去重。先马再说

 1 class Solution {
 2 // private:
 3 //     struct node{
 4 //         int a,b,c;
 5 //         node(){}
 6 //         node(int x,int y,int z):a(x),b(y),c(z){}
 7 //         bool operator<(const node &n)const{
 8 //             if(a==n.a&&b==n.b&&c==n.c) return false;
 9 //             return true;
10 //         }
11 //     };
12 public:
13     vector<vector<int> > threeSum(vector<int>& nums) {
14         vector<vector<int> > v;
15         if(nums.size()<3) return v;
16         sort(nums.begin(),nums.end());
17         //set<node> s;
18         for(int i=0;i<nums.size();i++){
19             if(i>0&&nums[i]==nums[i-1]) continue;
20             int j=i+1,k=nums.size()-1;
21             while(j<k){
22                 int sum=nums[i]+nums[j]+nums[k];
23                 if(sum==0){
24                     vector<int> vv;
25                     vv.push_back(nums[i]);
26                     vv.push_back(nums[j]);
27                     vv.push_back(nums[k]);
28                     v.push_back(vv);
29     //                 node no(nums[i],nums[j],nums[k]);
30     //                 if(s.find(no)==s.end()){
31                 //     //cout<<"ha"<<endl;
32     //                     s.insert(no);
33     //                 }
34                     int tmp=nums[j];
35                     while(nums[j]==tmp) j++;
36                     continue;
37                 }
38                 if(sum<0) j++;
39                 else k--;
40             }
41         }
42 //         for(set<node>::iterator it=s.begin();it!=s.end();it++){
43 //             vector<int> vv;
44 //             vv.push_back(it->a);
45 //             vv.push_back(it->b);
46 //             vv.push_back(it->c);
47 //             v.push_back(vv);
48 //         }
49        // cout<<"*********"<<endl;
50 //         for(int i=0;i<v.size();i++){
51 //             cout<<v[i][0]<<" "<<v[i][1]<<" "<<v[i][2]<<endl;
52 //         }
53         return v;
54     }
55 };

时间： 2024-11-07 02:27:43

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