hdu 5423 树上dfs 水题

#include<stdio.h>
#include<string>
#include<map>
#include<vector>
#include<cmath>
#include<stdlib.h>
#include<string.h>
#include<algorithm>
#include<iostream>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
const int N=1e3+10;
const int MOD=1e9+7;
int n,m,k,up;
int dep
;
int cnt
;
vector<int> G
;
void dfs(int u,int f){
for(int i=0;i<G[u].size();i++){
int v=G[u][i];
if(v==f) continue;
dep[v]=dep[u]+1;
cnt[dep[v]]++;
dfs(v,u);
}
}
int main(){
#ifndef ONLINE_JUDGE
freopen("aaa","r",stdin);
#endif
int T;
while(~scanf("%d",&n)){
int u,v;
rep(i,n) G[i].clear();
memset(cnt,0,sizeof cnt);
rep(i,n-1) cin>>u>>v,G[u-1].push_back(v-1),G[v-1].push_back(u-1);
dep[0]=0;
cnt[0]=1;
dfs(0,-1);
bool ok=false;
rep(i,n) ok|= cnt[i]>1 && cnt[i+1]>0;
cout<<(ok?"NO":"YES")<<endl;
}
return 0;
}