【最短路+dijkstra+floyd+spfa】1596 find the safest road

Dijkstra 算法

/* THE PROGRAM IS MADE BY PYY */
/*----------------------------------------------------------------------------//
Copyright (c) 2011 panyanyany All rights reserved.

URL   : http://acm.hdu.edu.cn/showproblem.php?pid=1596 Name  : 1596 find the safest road

Date  : Sunday, January 22, 2012
Time Stage : half an hour

Result:
5286524	2012-01-22 16:22:38	Accepted	1596
1015MS	6632K	1962 B
C++	pyy

Test Data :

Review :
//----------------------------------------------------------------------------*/

#include
#include
#include

#include
#include
#include

using namespace std ;

#define INF        (-1)
#define MAXN       1002

typedef __int64    LL ;

#define min(x, y)    ((x) < (y) ? (x) : (y))
#define max(x, y)    ((x) > (y) ? (x) : (y))
#define MEM(a, v)    memset (a, v, sizeof (a))

bool	used[MAXN] ;

int		n, q ;
double	map[MAXN][MAXN], dist[MAXN] ;

double dijkstra (const int beg, const int end)
{
int i, j ;
int iMinPath ;
double MaxSafe ;

MEM (used, 0) ;
for (i = 1 ; i <= n ; ++i)
dist[i] = map[beg][i] ;

for (i = 1 ; i <= n ; ++i)
{
iMinPath = 1 ;
MaxSafe = 0 ;
for (j = 1 ; j <= n ; ++j)
{
if (used[j] || dist[j] == 0)
continue ;
if (dist[j] > MaxSafe)
{
iMinPath = j ;
MaxSafe = dist[j] ;
}
}
used[iMinPath] = 1 ;
for (j = 1 ; j <= n ; ++j)
{
if (used[j] || dist[iMinPath] == 0 || map[iMinPath][j] == 0)
continue ;
if (dist[j] == 0 || dist[j] < dist[iMinPath] * map[iMinPath][j])
dist[j] = dist[iMinPath] * map[iMinPath][j] ;
}
}
return dist[end] ;
}

int main ()
{
int i, j ;
int x, y ;
double ret ;
while (~scanf ("%d", &n))
{
for (i = 1 ; i <= n ; ++i)
for (j = 1 ; j <= n ; ++j)
{
scanf ("%lf", &map[i][j]) ;
}

scanf ("%d", &q) ;
for (i = 1 ; i <= q ; ++i)
{
scanf ("%d%d", &x, &y) ;
ret = dijkstra (x, y) ;
if (ret == 0)
puts ("What a pity!") ;
else
printf ("%.3lf\n", ret) ;
}
}
return 0 ;
}

Floyd 算法

/* THE PROGRAM IS MADE BY PYY */
/*----------------------------------------------------------------------------//
Copyright (c) 2011 panyanyany All rights reserved.

URL   : http://acm.hdu.edu.cn/showproblem.php?pid=1596 Name  : 1596 find the safest road

Date  : Sunday, January 22, 2012
Time Stage : half an hour

Result:
5286856	2012-01-22 19:02:13	Accepted	1596
3484MS	6620K	1456 B
C++	pyy

Test Data :

Review :

//----------------------------------------------------------------------------*/

#include
#include
#include
#include

#include
#include
#include

using namespace std ;

#define INF        (-1)
#define MAXN       1002

typedef __int64    LL ;

#define min(x, y)    ((x) < (y) ? (x) : (y))
#define max(x, y)    ((x) > (y) ? (x) : (y))
#define MEM(a, v)    memset (a, v, sizeof (a))

int		n, q ;
double	map[MAXN][MAXN] ;

void floyd ()
{
int i, j, k ;
double d ;
for (k = 1 ; k <= n ; ++k)
for (i = 1 ; i <= n ; ++i)
for (j = 1 ; j <= n ; ++j)
{
// 像这种数据这么大的题（n<=1000），加多条判断语句都会超时……
// 之前这里就是加了一条判断，结果就超时了……无限TLE
d = map[i][k] * map[k][j] ;
if (map[i][j] < d)
map[i][j] = d ;
}
}

int main ()
{
int i, j ;
int x, y ;
double ret ;

while (~scanf ("%d", &n))
{
for (i = 1 ; i <= n ; ++i)
for (j = 1 ; j <= n ; ++j)
{
scanf ("%lf", &map[i][j]) ;
}

floyd () ;
scanf ("%d", &q) ;
for (i = 1 ; i <= q ; ++i)
{
scanf ("%d%d", &x, &y) ;
ret = map[x][y] ;
if (ret == 0)
puts ("What a pity!") ;
else
printf ("%.3lf\n", ret) ;
}
}
return 0 ;
}

Spfa 算法

/* THE PROGRAM IS MADE BY PYY */
/*----------------------------------------------------------------------------//
Copyright (c) 2011 panyanyany All rights reserved.

URL   :
Name  :

Date  :
Time Stage :

Result:
5287003	2012-01-22 21:15:06	Accepted	1596
1046MS	6656K	1783 B
C++	pyy

Test Data :

Review :

//----------------------------------------------------------------------------*/

#include
#include
#include
#include

#include
#include
#include

using namespace std ;

#define INF        (-1)
#define MAXN       1002

typedef __int64    LL ;

#define min(x, y)    ((x) < (y) ? (x) : (y))
#define max(x, y)    ((x) > (y) ? (x) : (y))
#define MEM(a, v)    memset (a, v, sizeof (a))

bool	used[MAXN] ;

int		n, q ;
double	map[MAXN][MAXN], dist[MAXN] ;

double spfa (const int beg, const int end)
{
int i, t ;
double d ;
queue	q ;

MEM (used, 0) ;
MEM (dist, 0) ;

q.push (beg) ;
used[beg] = 1 ;
dist[beg] = 1 ;	// 记得要初始化出发点为1

while (!q.empty ())
{
t = q.front () ;
q.pop () ;

for (i = 1 ; i <= n ; ++i)
{
d = dist[t] * map[t][i] ;
if (dist[i] < d)
{
dist[i] = d ;
if (!used[i])
{
q.push (i) ;
used[i] = 1 ; // 第一次忘了这个，死循环
}
}
}
used[t] = 0 ;
}
return dist[end] ;
}

int main ()
{
int i, j ;
int x, y ;
double ret ;

while (~scanf ("%d", &n))
{
for (i = 1 ; i <= n ; ++i)
for (j = 1 ; j <= n ; ++j)
{
scanf ("%lf", &map[i][j]) ;
}

scanf ("%d", &q) ;
for (i = 1 ; i <= q ; ++i)
{
scanf ("%d%d", &x, &y) ;
ret = spfa (x, y) ;
if (ret == 0)
puts ("What a pity!") ;
else
printf ("%.3lf\n", ret) ;
}
}
return 0 ;
}