二分图判断——sgu 172. eXam
自己的代码：
用到了ＳＴＬ实现：
把两个二分集合分别保存在两个set容器里
在用queue实现可以对后面有影响的组合先进入set容器
View Code
#include
<
stdio.h
>
#include
<
set
>
#include
<
queue
>
#include
<
algorithm
>
#include
<
iostream
>
using
namespace
std;
char
hash[
209
][
209
];
bool
x[
30009
];
struct
data
{
int
a,b;
};
int
cmp(data x,data y)
{
return
x.a
<
y.a;
}
int
main()
{
int
n,m;
scanf(
"
%d%d
"
,
&
n,
&
m);
set
<
int
>
set1;
set
<
int
>
set2;
queue
<
data
>
qq;
int
i,j;
for
(i
=
1
;i
<=
n;i
++
)
{
for
(j
=
1
;j
<=
n;j
++
)
{
hash[i][j]
=
0
;
}
}
data t;
for
(i
=
0
;i
<
m;i
++
)
{
int
a,b;
scanf(
"
%d%d
"
,
&
a,
&
b);
t.a
=
a;
t.b
=
b;
qq.push(t);
}
bool
cuo
=
0
;
t
=
qq.front();
qq.pop();
set1.insert(t.a);
set2.insert(t.b);
if
(t.a
==
t.b)
{
printf(
"
no\n
"
);
return
0
;
}
x[t.b]
=
1
;
while
(
!
qq.empty())
{
t
=
qq.front();
qq.pop();
if
(set1.find(t.a)
!=
set1.end()
&&
set1.find(t.b)
!=
set1.end())
{
cuo
=
1
;
break
;
}
if
(set2.find(t.a)
!=
set2.end()
&&
set2.find(t.b)
!=
set2.end())
{
cuo
=
1
;
break
;
}
if
(set1.find(t.a)
!=
set1.end())
{
if
(set2.find(t.b)
==
set2.end())
{
set2.insert(t.b);
x[t.b]
=
1
;
}
continue
;
}
if
(set2.find(t.a)
!=
set2.end())
{
set1.insert(t.b);
continue
;
}
if
(set1.find(t.b)
!=
set1.end())
{
if
(set2.find(t.a)
==
set2.end())
{
set2.insert(t.a);
x[t.a]
=
1
;
}
continue
;
}
if
(set2.find(t.b)
!=
set2.end())
{
set1.insert(t.a);
continue
;
}
if
(hash[t.a][t.b]
<
100
)
//
一开始hash[t.a][t.b]==0会错是因为可能要先知道最后一个
{
//
然后知道最后第二个……只一次就会只考虑到最后一次……开100也只是保守数
hash[t.a][t.b]
++
;
qq.push(t);
}
else
{
set1.insert(t.a);
set2.insert(t.b);
x[t.b]
=
1
;
}
}
if
(cuo
==
0
)
{
int
add
=
0
;
printf(
"
yes\n
"
);
for
(i
=
1
;i
<=
n;i
++
)
{
if
(x[i]
==
0
)
add
++
;
}
printf(
"
%d\n
"
,add);
for
(i
=
1
;i
<=
n;i
++
)
{
if
(x[i]
==
0
)
{
printf(
"
%d
"
,i);
break
;
}
}
for
(i
=
i
+
1
;i
<=
n;i
++
)
{
if
(x[i]
==
0
)
printf(
"
%d
"
,i);
}
printf(
"
\n
"
);
}
else
{
printf(
"
no\n
"
);
}
return
0
;
}
通用的DFS算法：
View Code
#include
<
stdio.h
>
#include
<
iostream
>
using
namespace
std;
const
int
maxn
=
201
;
int
n, m, color[maxn];
bool
g[maxn][maxn];
bool
dfs(
int
now)
{
if
(color[now]
==-
1
)color[now]
=
0
;
for
(
int
i
=
1
;i
<=
n;i
++
){
if
(i
==
now
||!
g[i][now])
continue
;
if
(color[i]
!=-
1
&&
color[i]
==
color[now])
return
false
;
else
if
(color[i]
==-
1
)
{
color[i]
=
(color[now]
^
1
);
if
(
!
dfs(i))
return
false
;
}
}
return
true
;
}
int
main()
{
scanf(
"
%d %d
"
,
&
n,
&
m);
int
x, y,i;
for
(i
=
1
; i
<=
n; i
++
) color[i]
=-
1
;
for
(i
=
1
; i
<=
m; i
++
){
scanf(
"
%d %d
"
,
&
x,
&
y);
g[x][y]
=
g[y][x]
=
true
;
}
for
(i
=
1
; i
<=
n; i
++
)
{
if
(color[i]
==-
1
)
if
(
!
dfs(i))
{
printf(
"
no\n
"
);
return
0
;
}
}
printf(
"
yes\n
"
);
int
s
=
0
;
for
(i
=
1
;i
<=
n;i
++
)
if
(color[i]
==
0
)s
++
;
printf(
"
%d\n
"
,s);
for
(i
=
1
;i
<=
n;i
++
)
if
(color[i]
==
0
){printf(
"
%d
"
,i);
break
;}
for
(i
=
i
+
1
;i
<=
n;i
++
)
if
(color[i]
==
0
){printf(
"
%d
"
,i);}
printf(
"
\n
"
);
return
0
;
}