[英]Weird thing while solving n-queens
因此,我正在解決n皇后問題,並編寫了此回溯解決方案。
def isSafe(row, col, board):
print board
for i in range(col):
if board[row][i] == 'Q':
print 'faled here'
return False
r_row = row-1
c_col = col-1
while r_row >= 0 and c_col >=0:
if board[c_row][c_col] == 'Q':
return False
c_row -=1
c_col -=1
row = row-1
col = col-1
while row < len(board) and col >=0:
if board[row][col] == 'Q':
return False
row+=1
col-=1
return True
def solveNQueen(column, board):
if column == len(board[0]):
print board
return True
for each_row in range(len(board)):
print each_row,column
if isSafe(each_row,column,board):
print board,'before'
board[each_row][column] = 'Q'
print board,' after'
if solveNQueen(column+1,board):
return True
else:
board[each_row][column] = 0
print 'failed'
return False
board = [[0]*5]*5
print solveNQueen(0,board)
奇怪的是我在第34、35和36行中寫道:
print board,'before'
board[each_row][column] = 'Q'
print board,' after'
該語句將同一列中的所有索引更改為“ Q”,而不是在特定的行和列索引處將其更改。
從輸出:
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]] before
[['Q', 0, 0, 0, 0], ['Q', 0, 0, 0, 0], ['Q', 0, 0, 0, 0], ['Q', 0, 0, 0, 0], ['Q', 0, 0, 0, 0]] after
這是怎么回事? 還是我只是喝醉了?
問題是board = [[0]*5]*5
。 這將為您提供五個零的相同列表的五個副本。
一種可能的解決方法:
board = [x[:] for x in [[0] * 5] * 5]
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