P2661 信息传递

P2661 信息传递
dfs求最小环，要加时间戳，记录这个点是哪一次被dfs到的。]

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<set>
#include<map>
#include<stack>
#include<cstring>
#define inf 2147483647
#define For(i,a,b) for(register int i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()
//by war
//2017.11.5
using namespace std;
int n;
bool vis[200010];
int x;
int ans;
int d[200010];
int t[200010];
struct node
{
    int n;
    node *next;
}*e[200010];
void in(int &x)
{
    int y=1;
    char c=g();x=0;
    while(c<'0'||c>'9')
    {
    if(c=='-')
    y=-1;
    c=g();
    }
    while(c<='9'&&c>='0')x=(x<<1)+(x<<3)+c-'0',c=g();
    x*=y;
}
void o(int x)
{
    if(x<0)
    {
        p('-');
        x=-x;
    }
    if(x>9)o(x/10);
    p(x%10+'0');
}

void push(int x,int y)
{
    node *p;
    p=new node();
    p->n=y;
    if(e[x]==NULL)
    e[x]=p;
    else
    {
        p->next=e[x]->next;
        e[x]->next=p;
    }
}

void dfs(int now,int dis,int Time)
{
    d[now]=dis;
    vis[now]=true;
    t[now]=Time;
    for(node *i=e[now];i!=NULL;i=i->next)
    if(vis[i->n])
    {
    if(t[now]==t[i->n])
    ans=min(ans,d[now]-d[i->n]+1);    
    }    
    else    
    dfs(i->n,dis+1,Time);
}

int main()
{
    in(n);
    For(i,1,n)
    {
        in(x);
        push(i,x);
    }
    ans=inf;
    For(i,1,n)
    {
        if(!vis[i])
        {
        t[i]=i;
        dfs(i,0,i);    
        }
    }
    o(ans);
     return 0;
}