D. J.:

- Added the leetcode problem and solution for 37

Author: nobodyPerfecZ

README.md

@@ -88,6 +88,7 @@
 - [34 Find First and Last Position of Element in Sorted Array](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/description/)
 - [35 Search Insert Position](https://leetcode.com/problems/search-insert-position/description/)
 - [36 Valid Sudoku](https://leetcode.com/problems/valid-sudoku/description/)
+- [37 Sudoku Solver](https://leetcode.com/problems/sudoku-solver/description/)
 - [39 Combination Sum](https://leetcode.com/problems/combination-sum/description/)
 - [42 Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/description/)
 - [45 Jump Game II](https://leetcode.com/problems/jump-game-ii/description/)

awesome_python_leetcode/_37_sudoku_solver.py

@@ -0,0 +1,56 @@
+from typing import List
+
+
+class Solution:
+    """Base class for all LeetCode Problems."""
+
+    def solveSudoku(self, board: List[List[str]]) -> None:
+        """
+        Write a program to solve a Sudoku puzzle by filling the empty cells.
+
+        A sudoku solution must satisfy all of the following rules:
+        1. Each of the digits 1-9 must occur exactly once in each row.
+        2. Each of the digits 1-9 must occur exactly once in each column.
+        3. Each of the digits 1-9 must occur exactly once in each of the 9 3x3
+        sub-boxes of the grid.
+
+        The '.' character indicates empty cells.
+        """
+        # Time complexity: O(9^81)
+        # Space complexity: O(9^81)
+        # Compute remaining rows, cols and squares
+        rows = {i: set([str(val) for val in range(1, 10)]) for i in range(0, 9)}
+        cols = {i: set([str(val) for val in range(1, 10)]) for i in range(0, 9)}
+        squares = {i: set([str(val) for val in range(1, 10)]) for i in range(0, 9)}
+        for row in range(len(board)):
+            for col in range(len(board[row])):
+                if board[row][col] == ".":
+                    continue
+                square = 3 * (row // 3) + col // 3
+                rows[row].remove(board[row][col])
+                cols[col].remove(board[row][col])
+                squares[square].remove(board[row][col])
+
+        def dfs(row: int, col: int) -> bool:
+            new_col = (col + 1) % 9
+            new_row = row + 1 if new_col == 0 else row
+            if row >= 9:
+                return True
+            if board[row][col] != ".":
+                return dfs(new_row, new_col)
+            square = 3 * (row // 3) + col // 3
+            visited = rows[row].intersection(cols[col], squares[square])
+            for val in visited:
+                board[row][col] = val
+                rows[row].remove(val)
+                cols[col].remove(val)
+                squares[square].remove(val)
+                if dfs(new_row, new_col):
+                    return True
+                board[row][col] = "."
+                rows[row].add(val)
+                cols[col].add(val)
+                squares[square].add(val)
+            return False
+
+        return dfs(0, 0)

tests/test_37_sudoku_solver.py

@@ -0,0 +1,40 @@
+from typing import List
+
+import pytest
+
+from awesome_python_leetcode._37_sudoku_solver import Solution
+
+
+@pytest.mark.parametrize(
+    argnames=["board", "expected"],
+    argvalues=[
+        (
+            [
+                ["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"],
+            ],
+            [
+                ["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"],
+            ],
+        )
+    ],
+)
+def test_func(board: List[List[str]], expected: List[List[str]]):
+    """Tests the solution of a LeetCode problem."""
+    Solution().solveSudoku(board)
+    assert board == expected