poj1308
简单题
View Code
#include
<
iostream
>
#include
<
cstdio
>
#include
<
cstdlib
>
#include
<
cstring
>
using
namespace
std;
#define
maxn 1006
struct
Edge
{
int
v, next;
}edge[
1000005
];
int
name[maxn];
int
n, ecount, tot, root;
int
in
[maxn];
int
head[maxn];
bool
vis[maxn];
bool
ok;
void
addedge(
int
a,
int
b)
{
edge[ecount].next
=
head[a];
edge[ecount].v
=
b;
head[a]
=
ecount;
in
[b]
++
;
ecount
++
;
}
int
find(
int
a)
{
for
(
int
i
=
0
; i
<
n; i
++
)
if
(name[i]
==
a)
return
i;
name[n
++
]
=
a;
return
n
-
1
;
}
void
dfs(
int
root)
{
vis[root]
=
true
;
tot
++
;
for
(
int
i
=
head[root]; i
!=
-
1
; i
=
edge[i].next)
{
if
(vis[edge[i].v])
{
ok
=
false
;
return
;
}
if
(
!
ok)
return
;
dfs(edge[i].v);
}
}
int
main()
{
//
freopen("t.txt", "r", stdin);
int
t
=
0
;
while
(
1
)
{
t
++
;
memset(
in
,
0
,
sizeof
(
in
));
memset(head,
-
1
,
sizeof
(head));
memset(vis,
0
,
sizeof
(vis));
ecount
=
0
;
n
=
0
;
tot
=
0
;
ok
=
true
;
int
a, b;
scanf(
"
%d%d
"
,
&
a,
&
b);
if
(a
<
0
&&
b
<
0
)
return
0
;
if
(a
==
0
&&
b
==
0
)
{
printf(
"
Case %d is a tree.\n
"
, t);
continue
;
}
a
=
find(a);
b
=
find(b);
addedge(a, b);
while
(
1
)
{
scanf(
"
%d%d
"
,
&
a,
&
b);
if
(a
==
0
&&
b
==
0
)
break
;
a
=
find(a);
b
=
find(b);
addedge(a, b);
}
root
=
-
1
;
for
(
int
i
=
0
; i
<
n; i
++
)
if
(
in
[i]
==
0
)
root
=
i;
if
(root
>=
0
)
dfs(root);
if
(ok
&&
tot
==
n
&&
root
>=
0
)
printf(
"
Case %d is a tree.\n
"
, t);
else
printf(
"
Case %d is not a tree.\n
"
, t);
}
return
0
;
}