mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
45 lines
1.1 KiB
C++
45 lines
1.1 KiB
C++
|
#include <iostream>
|
||
|
|
#include <stdio.h>
|
||
|
|
#include <string.h>
|
||
|
|
#include <algorithm>
|
||
|
|
using namespace std;
|
||
|
|
int s[1005][1005],sum[1005],dis[1005];
|
||
|
|
int n;
|
||
|
|
void dfs(int x,int num){
|
||
|
|
int i;
|
||
|
|
dis[x]=num;
|
||
|
|
for(i=1;i<=n;i++)
|
||
|
|
if(s[x][i]&&!dis[i])
|
||
|
|
dfs(i,num+1);
|
||
|
|
}
|
||
|
|
int main(){
|
||
|
|
int i,a,b,ans;
|
||
|
|
while(scanf("%d",&n)!=EOF){
|
||
|
|
memset(s,0,sizeof(s));
|
||
|
|
memset(sum,0,sizeof(sum));
|
||
|
|
memset(dis,0,sizeof(dis));
|
||
|
|
for(i=1;i<=n-1;i++){
|
||
|
|
scanf("%d%d",&a,&b);
|
||
|
|
s[a][b]=s[b][a]=1;
|
||
|
|
}
|
||
|
|
dfs(1,1);
|
||
|
|
for(i=1;i<=n;i++)
|
||
|
|
sum[dis[i]]++;
|
||
|
|
ans=0;
|
||
|
|
for(i=1;i<=n;i++){
|
||
|
|
if(sum[i]==1)
|
||
|
|
ans++;
|
||
|
|
else{
|
||
|
|
if(sum[i+1]==0)
|
||
|
|
ans=n;
|
||
|
|
break;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
if(ans==n)
|
||
|
|
printf("YES\n");
|
||
|
|
else
|
||
|
|
printf("NO\n");
|
||
|
|
}
|
||
|
|
return 0;
|
||
|
|
}
|