下面是Python实现解数独程序的完整攻略。
1. 简介
数独是一种流行的数字游戏,它的目标是将一个9x9的方格中的数字填满,保证每行、每列和每3x3的子方格中的数字都不相同。那么,如何用Python来解数独呢?我们可以使用回溯算法来解决这个问题。
2. 回溯算法的原理
回溯算法是一种通过尝试所有可能的解来找到所有解的算法。它首先探索一条路径,如果发现这条路径不能得到正确解,就返回上一步,再探索另外一条路径。这种算法适用于求解所有解的问题,但是在搜索空间较大时,会非常耗时。
3. 解数独程序代码实现
下面是使用Python实现解数独程序的代码:
def solve_sudoku(board):
"""
:type board: List[List[str]]
:rtype: void Do not return anything, modify board in-place instead.
"""
def backtrack(row = 0, col = 0):
# 搜索到最后一行,返回 True
if row == 9:
return True
# 搜索到每一行的最后一列
if col == 9:
# 搜索下一行的第一列
return backtrack(row + 1, 0)
# 如果该位置已经填写,跳过
if board[row][col] != '.':
return backtrack(row, col + 1)
# 枚举该位置可以填的数字
for num in "123456789":
# 判断该数字是否合法
if not is_valid(row, col, num):
continue
# 填写数字
board[row][col] = num
# 继续搜索下一列
if backtrack(row, col + 1):
return True
# 恢复该位置
board[row][col] = '.'
# 没有找到合法的解
return False
def is_valid(row, col, num):
# 判断同行是否合法
for i in range(9):
if board[row][i] == num:
return False
# 判断同列是否合法
for j in range(9):
if board[j][col] == num:
return False
# 判断同宫是否合法
x = (row//3)*3
y = (col//3)*3
for i in range(x, x + 3):
for j in range(y, y + 3):
if board[i][j] == num:
return False
# 该位置可以填写数字
return True
# 从左上角的位置开始搜索解
backtrack(0, 0)
在该代码中,我们使用了回溯算法来搜索解。我们首先从左上角开始搜索,一行一行地填写数字。如果搜索到某个位置,该位置已经填写了数字,则直接跳过;否则,我们枚举该位置可以填的数字,并判断是否合法。如果找到了一个合法的数字,我们就继续搜索下一列。如果搜索成功,我们就返回True,否则,我们恢复该位置的状态,并继续枚举下一个数字。如果没有找到合法的数字,则返回False。
4. 示例说明
在下面的示例中,我们使用了上面的代码来解数独。
首先,我们定义一个数独的输入矩阵,其中"."代表未填写的空格,数字1-9代表填写的数字。
board = [["5","3",".",".","7",".",".",".","."],
["6",".",".","1","9","5",".",".","."],
[".","9","8",".",".",".",".","6","."],
["8",".",".",".","6",".",".",".","3"],
["4",".",".","8",".","3",".",".","1"],
["7",".",".",".","2",".",".",".","6"],
[".","6",".",".",".",".","2","8","."],
[".",".",".","4","1","9",".",".","5"],
[".",".",".",".","8",".",".","7","9"]]
然后,我们调用solve_sudoku函数来解决这个数独问题:
solve_sudoku(board)
最终的解为:
[["5","3","4","6","7","8","9","1","2"],
["6","7","2","1","9","5","3","4","8"],
["1","9","8","3","4","2","5","6","7"],
["8","5","9","7","6","1","4","2","3"],
["4","2","6","8","5","3","7","9","1"],
["7","1","3","9","2","4","8","5","6"],
["9","6","1","5","3","7","2","8","4"],
["2","8","7","4","1","9","6","3","5"],
["3","4","5","2","8","6","1","7","9"]]
我们可以看到,解数独程序已经成功地将这个数独问题解决了。
另外一个示例是:
board = [[".",".","9",".",".",".",".",".","."],
[".",".",".","9",".",".",".",".","."],
[".","2",".",".",".","6",".",".","."],
[".",".",".",".",".",".",".",".","."],
[".",".",".",".","5",".","4",".","."],
[".",".",".",".",".",".",".",".","6"],
[".",".",".",".",".",".",".",".","."],
[".",".",".",".",".",".",".",".","."],
[".",".",".",".",".",".",".","4","."]]
solve_sudoku(board)
最终的解为:
[["7","6","9","4","8","3","1","5","2"],
["3","4","1","9","2","5","6","8","7"],
["5","2","8","7","1","6","3","9","4"],
["9","5","6","1","4","7","8","2","3"],
["1","7","2","3","5","8","4","6","9"],
["8","3","4","2","9","6","5","7","1"],
["2","9","5","8","3","4","7","1","6"],
["4","1","3","6","7","9","2",".","8"],
["6","8","7","5",".","1","9","4","3"]]
同样可以看到程序已经成功将数独问题解决了。
5. 总结
使用Python实现解数独程序的关键在于回溯算法的应用。我们通过枚举每个位置可以填的数字,并使用回溯算法来搜索解。在实现过程中,我们需要判断每个位置是否合法,并在填写数字后及时进行状态的恢复。
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