UVA-10938 - Flea circus(dfs)

// File Name: 10938.cpp
// Author: Zlbing
// Created Time: 2013/4/19 14:57:26

#include<iostream>
#include<string>
#include<algorithm>
#include<cstdlib>
#include<cstdio>
#include<set>
#include<map>
#include<vector>
#include<cstring>
#include<stack>
#include<cmath>
#include<queue>
using namespace std;
#define CL(x,v); memset(x,v,sizeof(x));
#define INF 0x3f3f3f3f
#define LL long long
#define REP(i,r,n) for(int i=r;i<=n;i++)
#define RREP(i,n,r) for(int i=n;i>=r;i--)
const int MAXN=5e3+100;
vector<int> G[MAXN];
int vis[MAXN],P[MAXN];
int dfs(int u,int s,int k)
{
vis[u]=1;
if(u==s){
P[u]=k;
return true;
}
for(int i=0;i<G[u].size();i++)
{
int v=G[u][i];
if(vis[v])continue;
if(dfs(v,s,k+1)){
//printf("u--%d v---%d\n",u,v);
P[u]=k;
return true;
}
}
return false;
}
int main()
{
int n;
while(~scanf("%d",&n))
{
if(!n)break;
REP(i,1,n)G[i].clear();
REP(i,1,n-1)
{
int a,b;
scanf("%d%d",&a,&b);
G[a].push_back(b);
G[b].push_back(a);
}
int m;
scanf("%d",&m);
REP(i,1,m)
{
int a,b;
scanf("%d%d",&a,&b);
CL(P,0);
CL(vis,0);
dfs(a,b,1);
int t=P[b];
//    printf("tttt%d\n",t);
//REP(i,1,n)printf("P[%d]=%d\n",i,P[i]);
if(t%2)
{
printf("The fleas meet at ");
REP(i,1,n)
if(P[i]==(t+1)/2)
printf("%d.\n",i);
}
else{
printf("The fleas jump forever between ");

REP(i,1,n)
if(P[i]==t/2)a=i;
REP(i,1,n)
if(P[i]-1==t/2)b=i;
int m=min(a,b);
int mm=max(a,b);
printf("%d and %d.\n",m,mm);
}
}
}
return 0;
}