添加 0037.解数独 python3版本

添加 0037.解数独 python3版本

Author: jojoo15

problems/0037.解数独.md

@@ -287,7 +287,39 @@ class Solution {
 ```
 
 Python：
-
+```python3
+class Solution:
+    def solveSudoku(self, board: List[List[str]]) -> None:
+        """
+        Do not return anything, modify board in-place instead.
+        """
+        def backtrack(board):
+            for i in range(len(board)):  #遍历行
+                for j in range(len(board[0])):  #遍历列
+                    if board[i][j] != ".": continue
+                    for k in range(1,10):  #(i, j) 这个位置放k是否合适
+                        if isValid(i,j,k,board):
+                            board[i][j] = str(k)  #放置k
+                            if backtrack(board): return True  #如果找到合适一组立刻返回
+                            board[i][j] = "."  #回溯，撤销k
+                    return False  #9个数都试完了，都不行，那么就返回false
+            return True  #遍历完没有返回false，说明找到了合适棋盘位置了
+        def isValid(row,col,val,board):
+            for i in range(9):  #判断行里是否重复
+                if board[row][i] == str(val):
+                    return False
+            for j in range(9):  #判断列里是否重复
+                if board[j][col] == str(val):
+                    return False
+            startRow = (row // 3) * 3
+            startcol = (col // 3) * 3
+            for i in range(startRow,startRow + 3):  #判断9方格里是否重复
+                for j in range(startcol,startcol + 3):
+                    if board[i][j] == str(val):
+                        return False
+            return True
+        backtrack(board)
+```
 
 Go：