Submission #1689700

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Source Code Expand

#include<bits/stdc++.h>
#define pb push_back

using namespace std;

const int N=200005;
int n,U,R,dep[N],fa[N],m;
vector<int>er[N],eb[N];

void dfs(int x){for(int v:eb[x])if(v!=fa[x])fa[v]=x,dep[v]=dep[x]+1,dfs(v);}
inline bool check(int u,int v){
	if(dep[u]<dep[v]) swap(u,v);
	int d=0;
	while(++d<=2&&u!=v)if(dep[u]<dep[v])v=fa[v];else u=fa[u];
	return u==v;
}
void dfs(int x,int fa,int k){
	m=max(m,dep[x]);
	if(dep[x]<=k)return;
	for(int v:er[x])if(v!=fa){
		if(!check(x,v))puts("-1"),exit(0);
		dfs(v,x,k+1);
	}
}

int main(){
	scanf("%d%d%d",&n,&U,&R);
	for(int i=1,u,v;i<n;i++)scanf("%d%d",&u,&v),er[u].pb(v),er[v].pb(u);
	for(int i=1,u,v;i<n;i++)scanf("%d%d",&u,&v),eb[u].pb(v),eb[v].pb(u);
	dfs(R),dfs(U,0,0);
	printf("%d\n",m<<1);
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:27:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n,&U,&R);
                          ^
./Main.cpp:28:69: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  for(int i=1,u,v;i<n;i++)scanf("%d%d",&u,&v),er[u].pb(v),er[v].pb(u);
                                                                     ^
./Main.cpp:29:69: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  for(int i=1,u,v;i<n;i++)scanf("%d%d",&u,&v),eb[u].pb(v),eb[v].pb(u);
                                                                     ^

Judge Result