HDOJ 1269(Tarjan)

思路：Tarjan

/*=====================================================================
# Author: wangzhili
# Mail  : wangstdio.h@gmail.com
# QQ : 240130760
# Filename: tarjan.c
# Last modified: 2013-12-06 09:18
=====================================================================*/

#include<stdio.h>
#include<string.h>
typedef struct
{
    int to;
    int next;
}EdgeNode;
EdgeNode edge[100005];
int dfn[10005],low[10005];
int head[10005],vis[10005];
int stack[10005];
int top,ind,cnt,n,m;
int min(int x,int y)
{
    return x < y ? x : y;
}

void tarjan(int i)
{
    int j,v;
    dfn[i] = low[i] = ++ind;
    stack[++top] = i;
    vis[i] = 1;
    for(j = head[i]; j != -1;j = edge[j].next)
    {
        v = edge[j].to;
        if(!dfn[v])
        {
            tarjan(v);
            low[i] = min(low[i],low[v]);
        }
        else if(vis[v])
            low[i] = min(low[i],dfn[v]);
    }
    if(dfn[i] == low[i])
    {
        cnt ++;
        do
        {
            j = stack[top--];
            vis[j] = 0;
        }while(j != i);
    }
}
void solve()
{
    int i;
    cnt = 0;
    top = ind = 0;
    memset(dfn,0,sizeof(dfn));
    memset(vis,0,sizeof(vis));
    for(i = 1;i <= n;i ++)
    {
        if(!dfn[i])
            tarjan(i);
    }
    return ;
}

int main()
{
    int i,j;
    int a,b;
    freopen("in.c","r",stdin);
    while(~scanf("%d%d",&n,&m) && (m+n))
    {
        memset(head,-1,sizeof(head));
        for(i = 0;i < m;i ++)
        {
            scanf("%d%d",&a,&b);
            edge[i].to = b;
            edge[i].next = head[a];
            head[a] = i;
        }
        solve();
        if(cnt == 1)
            printf("Yes\n");
        else
            printf("No\n");
    }
    return 0;
}