poj 2762 Going from u to v or fr…

题意+思路 见前一博文

#include <stdio.h>

#include <string.h>

#define VM 1005

#define EM 6005

struct E

{

int
to,next;

}edge[EM];

struct E1

{

int
frm,to,next;

}edge1[EM];

int head[VM],head1[VM],indeg[VM],map[VM][VM];

int dfn[VM],low[VM],vis[VM],belong[VM],stack[VM];

int scc,cnt,top,p,n;

void addedge (int cu,int cv)

{

edge[p].to =
cv;

edge[p].next
= head[cu];

head[cu] =
p++;

}

void addedge1(int cu,int cv)

{

edge1[p].frm
= cu;

edge1[p].to
= cv;

edge1[p].next = head1[cu];

head1[cu] =
p ++;

}

void tarjan (int u)

{

int v;

dfn[u] =
low[u] = ++cnt;

stack[top++]
= u;

vis[u] =
1;

for (int i =
head[u];i != -1;i = edge[i].next)

{

v = edge[i].to;

if (!dfn[v])

{

tarjan(v);

low[u] = low[u] > low[v]?low[v]:low[u];

}

else if (vis[v]&&low[u]
> dfn[v])

low[u] = dfn[v];

}

if (dfn[u]
== low[u])

{

++scc;

do

{

v = stack[--top];

vis[v] = 0;

belong[v] = scc;

} while (u != v);

}

}

void sovle ()

{

int u;

scc = top =
cnt = 0;

memset
(dfn,0,sizeof(dfn));

memset
(vis,0,sizeof(vis));

for (u = 1;u
<= n;u ++)

if (!dfn[u])

tarjan(u);

}

int topo ()

{

int
u,v,i,cur,count = 0;;

for (u = 1;u
<= scc;u ++)

if (!indeg[u])

{

count ++;

cur = u;

}

if (count
> 1)

return 0;

int num =
scc;

while (num
--)

{

count = 0;

for (i = head1[cur];i != -1;i = edge1[i].next)

{

u = edge1[i].frm;

v = edge1[i].to;

//indeg[u] --;

indeg[v] --;

if (!indeg[v])

{

count ++;

cur = v;

}

}

if (count > 1)

return 0;

}

return
1;

}

int ans()

{

int
u,v,i,count = 0;

memset
(indeg,0,sizeof(indeg));

memset
(map,0,sizeof (map));

for (u = 1;u
<= n;u ++)

for (i = head[u];i != -1;i = edge[i].next)

{

v = edge[i].to;

int j,k;

j = belong[u];

k = belong[v];

if (j != k&& !map[j][k])

{

indeg[k] ++;

addedge1 (j,k);

map[j][k] = 1;

}

}

if
(topo())

return 1;

return
0;

}

int main ()

{

int
t,m,u,v;

scanf
("%d",&t);

while (t
--)

{

p = 0;

memset
(head1,-1,sizeof(head1));

memset (head,-1,sizeof(head));

scanf ("%d%d",&n,&m);

while (m --)

{

scanf ("%d%d",&u,&v);

addedge (u,v);

}

sovle ();

if (ans())

printf ("Yes\n");

else

printf("No\n");

}

return
0;

}