Submission #1687177

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Source Code Expand

#include<bits/stdc++.h>
#define N 200005
using namespace std;
int n,u,v,fa[N],fst[N],to[N],nxt[N],l,dep[N],dis[N],Ans,f[N],q[N];
struct T
{
	int x,y;
}a[N],b[N];
vector<int>e[N];
void link(int x,int y)
{
	to[++l]=y;nxt[l]=fst[x];fst[x]=l;
	to[++l]=x;nxt[l]=fst[y];fst[y]=l;
}
void dfs(int x)
{
	for (int i=fst[x];i;i=nxt[i])
		if (to[i]!=fa[x])
		{
			fa[to[i]]=x;
			dep[to[i]]=dep[x]+1;
			dfs(to[i]);
		}
}
int Gdis(int x,int y)
{
	if (x==y) return 0;
	if (fa[x]==y||fa[y]==x) return 1;
	if (fa[x]==fa[y]||fa[fa[x]]==y||fa[fa[y]]==x) return 2;
	return 3;
}
int main()
{
	scanf("%d%d%d",&n,&u,&v);
	//if (u==v){puts("0");,return 0;}
	for (int i=1;i<n;i++)
		scanf("%d%d",&a[i].x,&a[i].y);
	for (int i=1;i<n;i++)
	{
		scanf("%d%d",&b[i].x,&b[i].y);
		link(b[i].x,b[i].y);
	}
	dfs(v);
	for (int i=1;i<n;i++)
	{
		int tmp=Gdis(a[i].x,a[i].y);
		if (tmp==1)
		{
			e[a[i].x].push_back(a[i].y);
			e[a[i].y].push_back(a[i].x);
		}
		else if (tmp==2)
		{
			if (fa[a[i].x]!=v||fa[a[i].y]!=v)
			{
				e[a[i].x].push_back(a[i].y);
				e[a[i].y].push_back(a[i].x);
			}
		}
		else f[a[i].x]=f[a[i].y]=1;
	}
	memset(dis,0x3f,sizeof dis);
	int l=0,r=1;
	q[1]=u;dis[u]=0;
	while(l<r)
	{
		int t=q[++l];
		//cout<<t<<' '<<dis[t]<<endl;
		if (f[t]==1){puts("-1");return 0;}
		else Ans=max(Ans,dep[t]*2);
		for (int i=0;i<e[t].size();i++)
			if (dis[e[t][i]]>dis[t]+1&&dis[t]+1<dep[e[t][i]])
			{
				dis[e[t][i]]=dis[t]+1;
				q[++r]=e[t][i];
			}
	}
	printf("%d\n",Ans);
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:34:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d",&n,&u,&v);
                          ^
./Main.cpp:37:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d",&a[i].x,&a[i].y);
                                ^
./Main.cpp:40:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d",&b[i].x,&b[i].y);
                                ^

Judge Result