poj3159
spfa算法可以用栈代替队列，入栈时注意判断是否已在栈中。
开始以为是要找最长路，其实是要找最短路。
View Code
#include
<
iostream
>
#include
<
cstdio
>
#include
<
cstdlib
>
#include
<
cstring
>
using
namespace
std;
#define
maxn 30005
#define
maxm 150005
struct
Edge
{
int
v, w, next;
}edge[maxm];
int
n, m, head[maxn], mystack[maxn], edgenum, top, mytime[maxn];
bool
instack[maxn];
void
init()
{
edgenum
=
0
;
memset(head,
-
1
,
sizeof
(head));
for
(
int
i
=
0
; i
<
m; i
++
)
{
int
a, b, c;
scanf(
"
%d%d%d
"
,
&
a,
&
b,
&
c);
a
--
;
b
--
;
edge[edgenum].next
=
head[a];
edge[edgenum].v
=
b;
edge[edgenum].w
=
c;
head[a]
=
edgenum;
edgenum
++
;
}
}
void
work()
{
memset(instack,
0
,
sizeof
(instack));
memset(mytime,
-
1
,
sizeof
(mytime));
instack[
0
]
=
1
;
mystack[
0
]
=
0
;
mytime[
0
]
=
0
;
top
=
1
;
while
(top)
{
int
temp
=
mystack[
--
top];
instack[temp]
=
false
;
for
(
int
i
=
head[temp]; i
!=
-
1
; i
=
edge[i].next)
{
if
(mytime[edge[i].v]
==
-
1
||
mytime[edge[i].v]
>
mytime[temp]
+
edge[i].w)
{
mytime[edge[i].v]
=
mytime[temp]
+
edge[i].w;
if
(
!
instack[edge[i].v])
{
mystack[top
++
]
=
edge[i].v;
instack[edge[i].v]
=
true
;
}
}
}
}
printf(
"
%d\n
"
, mytime[n
-
1
]);
}
int
main()
{
//
freopen("D:\\t.txt", "r", stdin);
scanf(
"
%d%d
"
,
&
n,
&
m);
init();
work();
}