Python描述 LeetCode 37. 解数独
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Python描述 LeetCode 37. 解数独
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题目
编写一个程序,通过填充空格来解决数独问题。
数独的解法需 遵循如下规则:
- 数字
1-9
在每一行只能出现一次。 - 数字
1-9
在每一列只能出现一次。 - 数字
1-9
在每一个以粗实线分隔的3x3
宫内只能出现一次。(请参考示例图)
数独部分空格内已填入了数字,空白格用 '.'
表示。
示例 1:
输入: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"]]
输出:[["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"]]
解释:输入的数独如上图所示,唯一有效的解决方案如下所示:
提示:
board.length == 9
board[i].length == 9
board[i][j]
是一位数字或者'.'
- 题目数据 保证 输入数独仅有一个解
解题思路
DFS一路向前搜索,挨个将空格填上数字,当全部满足时,返回结束循环
Python描述
class Solution:
def solveSudoku(self, board: List[List[str]]) -> None:
"""
Do not return anything, modify board in-place instead.
"""
global complete_flag
line = [[0 for _ in range(10)] for __ in range(9)]
col = [[0 for _ in range(10)] for __ in range(9)]
jiu = [[[0 for _ in range(10)] for __ in range(3)] for ___ in range(3)]
complete_flag = False
# 初始化
for i in range(9):
for j in range(9):
tmp = int(board[i][j]) if board[i][j] != '.' else 0
if tmp == 0:
continue
line[i][tmp] += 1
col[j][tmp] += 1
jiu[i // 3][j // 3][tmp] += 1
def whether_fit(i, j, num):
# 检测当前位置是否能放num
return line[i][num] + col[j][num] + jiu[i // 3][j // 3][num] == 0
def dfs(i, j):
global complete_flag
if complete_flag:
return
if i == j == 8 and board[i][j] != '.':
complete_flag = True
return
if board[i][j] != '.':
n_j = (j + 1) % 9
n_i = i if n_j != 0 else i + 1
dfs(n_i, n_j)
return
for ch in "123456789":
tmp = int(ch)
if whether_fit(i, j, tmp):
board[i][j] = ch
line[i][tmp] += 1
col[j][tmp] += 1
jiu[i // 3][j // 3][tmp] += 1
n_j = (j + 1) % 9
n_i = i if n_j != 0 else i + 1
if n_i == 9:
complete_flag = True
return
dfs(n_i, n_j)
if complete_flag:
return
board[i][j] = "."
line[i][tmp] -= 1
col[j][tmp] -= 1
jiu[i // 3][j // 3][tmp] -= 1
dfs(0, 0)
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