something about my mistake.----p1475_push the boxes

 

Pushing Boxes

Time Limit: 2000MSMemory Limit: 131072KTotal Submissions: 1963Accepted: 754Special Judge

Description

Imagineyou are standing inside a two-dimensional maze composed of square cellswhich may or may not be filled with rock. You can move north, south,east or west one cell at a step. These moves are called walks.
One of the empty cells contains a box which can be moved to anadjacent free cell by standing next to the box and then moving in thedirection of the box. Such a move is called a push. The box cannot bemoved in any other way than by pushing, which means that if you push itinto a corner you can never get it out of the corner again.

One of the empty cells is marked as the target cell. Your job is tobring the box to the target cell by a sequence of walks and pushes. Asthe box is very heavy, you would like to minimize the number of pushes.Can you write a program that will work out the best such sequence?

Input

Theinput contains the descriptions of several mazes. Each maze descriptionstarts with a line containing two integers r and c (both <= 20)representing the number of rows and columns of the maze.

Following this are r lines each containing c characters. Eachcharacter describes one cell of the maze. A cell full of rock isindicated by a `#' and an empty cell is represented by a `.'. Yourstarting position is symbolized by `S', the starting position of thebox by `B' and the target cell by `T'.

Input is terminated by two zeroes for r and c.

Output

Foreach maze in the input, first print the number of the maze, as shown inthe sample output. Then, if it is impossible to bring the box to thetarget cell, print ``Impossible.''.

Otherwise, output a sequence that minimizes the number of pushes.If there is more than one such sequence, choose the one that minimizesthe number of total moves (walks and pushes). If there is still morethan one such sequence, any one is acceptable.

Print the sequence as a string of the characters N, S, E, W, n, s,e and w where uppercase letters stand for pushes, lowercase lettersstand for walks and the different letters stand for the directionsnorth, south, east and west.

Output a single blank line after each test case.

Sample Input

1 7
SB....T
1 7
SB..#.T
7 11
###########
#T##......#
#.#.#..####
#....B....#
#.######..#
#.....S...#
###########
8 4
....
.##.
.#..
.#..
.#.B
.##S
....
###T
0 0

Sample Output

Maze #1
EEEEE

Maze #2
Impossible.

Maze #3
eennwwWWWWeeeeeesswwwwwwwnNN

Maze #4
swwwnnnnnneeesssSSS

Source

Southwestern European Regional Contest 1997

if one has the commen sense of dp or bfs.

he can tell me that this one is not a dp_tree problem.

because the relationship of one grid and its adjecent ones is not father_son relationship, instead, the are in disorder ,

so it can't be solved using dp_tree model.

but i am so foolish and forgetable that i used this method , wa! and debug it for many hours.

Miss Carrot , you should think more clearly before code.!

ok ! you know you can!