Submission #27459600

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Source Code Expand

#include<bits/stdc++.h>
#define N 200005

int n,a,b;

std::vector<int> A[N],B[N];

int fa[N],dep[N];
inline void dfs(int u){
	dep[u]=dep[fa[u]]+1;
	for(auto v:B[u])
		if(v!=fa[u])
			fa[v]=u,dfs(v);
}

int f[N];
std::queue<int> q;

int ans;

int main(){
	scanf("%d%d%d",&n,&a,&b);
	for(int i=1;i<n;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		A[u].push_back(v),A[v].push_back(u);
	}
	for(int i=1;i<n;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		B[u].push_back(v),B[v].push_back(u);
	}
	dfs(b);
	f[a]=1;
	q.push(a);
	while(q.size()){
		int u=q.front();
		q.pop();
		ans=std::max(ans,dep[u]-1);
		for(auto v:A[u]){
			if(fa[u]!=fa[v]&&v!=fa[u]&&v!=fa[fa[u]]&&u!=fa[v]&&u!=fa[fa[v]])
				return puts("-1"),0;
			if(!f[v]&&dep[v]>f[u]+1){
				f[v]=f[u]+1;
				q.push(v);
			}
		}
	}
	printf("%d\n",ans<<1);
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:22:7: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   22 |  scanf("%d%d%d",&n,&a,&b);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~
./Main.cpp:25:8: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   25 |   scanf("%d%d",&u,&v);
      |   ~~~~~^~~~~~~~~~~~~~
./Main.cpp:30:8: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   30 |   scanf("%d%d",&u,&v);
      |   ~~~~~^~~~~~~~~~~~~~

Judge Result