daily

Author: Zanger67

my-submissions/h37.py

@@ -0,0 +1,63 @@
+class Solution:
+    def solveSudoku(self, board: List[List[str]]) -> None:
+        """
+        Do not return anything, modify board in-place instead.
+        """
+        board_squares = [[set(), set(), set()] for _ in range(3)]
+        board_rows = [set() for _ in range(9)]
+        board_cols = [set() for _ in range(9)]
+
+        for r in range(9) :
+            for c in range(9) :
+                if board[r][c] == '.' :
+                    continue
+                board_squares[r // 3][c // 3].add(board[r][c])
+                board_rows[r].add(board[r][c])
+                board_cols[c].add(board[r][c])
+
+        self._helper(board, board_squares, board_rows, board_cols)
+
+    def _helper(self, 
+                board: List[List[str]], 
+                board_squares, 
+                board_rows, 
+                board_cols, 
+                r: int = 0, 
+                c: int = 0) -> bool :
+        if r >= 9 :
+            return True
+
+        c_next = c + 1
+        r_next = r
+        if c_next > 8 :
+            c_next %= 9
+            r_next += 1
+
+        if board[r][c] != '.' :
+            return self._helper(board, board_squares, board_rows, board_cols, r_next, c_next)
+        for candidate in range(1, 10) :
+            candidate_str = str(candidate)
+            if (
+                candidate_str in board_squares[r // 3][c // 3] or
+                candidate_str in board_rows[r] or
+                candidate_str in board_cols[c]
+            ) :
+                continue
+
+            board[r][c] = candidate_str
+
+            board_squares[r // 3][c // 3].add(candidate_str)
+            board_rows[r].add(candidate_str)
+            board_cols[c].add(candidate_str)
+
+
+            if self._helper(board, board_squares, board_rows, board_cols, r_next, c_next) :
+                return True
+
+            board_squares[r // 3][c // 3].remove(candidate_str)
+            board_rows[r].remove(candidate_str)
+            board_cols[c].remove(candidate_str)
+
+
+        board[r][c] = '.'
+        return False