codeforces#572Div2 D1---Add On A Tree【思维】

 1 #include<cstdio>
 2 #include<cstdlib>
 3 #include<map>
 4 #include<set>
 5 #include<cstring>
 6 #include<algorithm>
 7 #include<vector>
 8 #include<cmath> 
 9 #include<stack>
10 #include<queue>
11 #include<iostream>
12 
13 #define inf 0x3f3f3f3f
14 using namespace std;
15 typedef long long LL;
16 typedef pair<int, int> pr;
17 
18 int n;
19 const int maxn = 1e5 + 5;
20 int deg[maxn];
21 
22 int main()
23 {
24     scanf("%d", &n);;
25     for(int i = 1; i < n; i++){
26         int u, v;
27         scanf("%d%d", &u, &v);
28         deg[u]++;
29         deg[v]++;
30     }
31     int ans = true;
32     for(int i = 1; i <= n; i++){
33         if(deg[i] == 2){
34             ans = false;
35             break;
36         }
37     }
38     if(ans){
39         printf("YES\n");
40     }
41     else{
42         printf("NO\n");
43     }
44     return 0;
45 }