45 lines
1.1 KiB
C++
45 lines
1.1 KiB
C++
#include <iostream>
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#include <stdio.h>
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#include <string.h>
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#include <algorithm>
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using namespace std;
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int s[1005][1005],sum[1005],dis[1005];
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int n;
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void dfs(int x,int num){
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int i;
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dis[x]=num;
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for(i=1;i<=n;i++)
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if(s[x][i]&&!dis[i])
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dfs(i,num+1);
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}
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int main(){
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int i,a,b,ans;
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while(scanf("%d",&n)!=EOF){
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memset(s,0,sizeof(s));
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memset(sum,0,sizeof(sum));
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memset(dis,0,sizeof(dis));
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for(i=1;i<=n-1;i++){
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scanf("%d%d",&a,&b);
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s[a][b]=s[b][a]=1;
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}
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dfs(1,1);
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for(i=1;i<=n;i++)
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sum[dis[i]]++;
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ans=0;
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for(i=1;i<=n;i++){
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if(sum[i]==1)
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ans++;
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else{
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if(sum[i+1]==0)
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ans=n;
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break;
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}
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}
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if(ans==n)
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printf("YES\n");
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else
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printf("NO\n");
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}
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return 0;
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}
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