OJ-Problems-Source/HDOJ/3313_autoAC.cpp
2016-09-01 20:54:35 +08:00

79 lines
1.8 KiB
C++

#include <iostream>
#include <cstdio>
#include <queue>
#include <cstring>
#include <cstdlib>
using namespace std;
#define MAXN 100010
int pre[MAXN],vis[MAXN],low[MAXN];
vector <int> e[MAXN];
int bfs1(int st,int et){
queue <int> q;
q.push(st);
vis[st]=1;pre[st]=-1;
while(!q.empty()){
int now=q.front();
q.pop();
for(int i=e[now].size()-1;i>=0;i--){
int next=e[now][i];
if(vis[next])continue;
vis[next]=1;
pre[next]=now;
if(next==et)return 1;
q.push(next);
}
}
return 0;
}
int bfs2(int u){
queue <int> q;
q.push(u);
int res=u;
vis[u]=1;
while(!q.empty()){
int now=q.front();
q.pop();
for(int i=e[now].size()-1;i>=0;i--){
int next=e[now][i];
if(vis[next])continue;
vis[next]=1;
if(low[next]==0)q.push(next);
else if(low[next]<low[res])res=next;
}
}
return res;
}
int main()
{
int n,m,st,et;
while(~scanf("%d%d",&n,&m)){
for(int i=0;i<=n;i++)
e[i].clear();
memset(vis,0,sizeof(vis));
memset(low,0,sizeof(low));
for(int i=0,x,y;i<m;i++){
scanf("%d%d",&x,&y);
e[x].push_back(y);
}
scanf("%d%d",&st,&et);
if(!bfs1(st,et)){
printf("%d\n",n);
continue;
}
int u=et,tot=1;
memset(vis,0,sizeof(vis));
while(u!=-1){
low[u]=tot++;
u=pre[u];
}
int cnt=1;
u=st;
while(u!=et){
u=bfs2(u);
++cnt;
}
printf("%d\n",cnt);
}
return 0;
}