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;
}