_

add: top20 system design concepts

Author: kimtth

Glossary.md

@@ -48,6 +48,10 @@
 
             🔹 Behavioral: here we have Command, Iterator, State, Strategy, ...
 
+1. Top 20 System Design Concepts
+
+    <img src="files/top20-system-design-concepts.png" alt="top-20-sys-design" width="400"/>
+
 1. Memory consistency model: [A Primer on Memory Consistency and Cache Coherence](https://link.springer.com/book/10.1007/978-3-031-01764-3)
 
     - **SC vs TSO vs Relaxed Memory Consistency**

files/algorithm_pattern/sudoku.py

@@ -0,0 +1,113 @@
+def is_valid(board, row, col, num):
+    # Check if num is in the same row or column
+    for i in range(3):
+        if board[row][i] == num or board[i][col] == num:
+            return False
+    return True
+
+
+def find_empty(board):
+    # Return the next empty cell (row, col) or None if full
+    for row in range(3):
+        for col in range(3):
+            if board[row][col] == 0:
+                return row, col
+    return None
+
+
+def solve_sudoku(board, depth=0):
+    indent = "  " * depth  # Visual indent for stack level
+    empty = find_empty(board)
+    
+    if not empty:
+        print(f"{indent}✔️ Solved at depth {depth}")
+        return True
+
+    row, col = empty
+    for num in range(1, 4):
+        if is_valid(board, row, col, num):
+            print(f"{indent}Trying {num} at ({row}, {col}) [depth {depth}]")
+            board[row][col] = num
+            print(f"{indent}Board state: {board}")
+
+            if solve_sudoku(board, depth + 1):
+                return True
+
+            print(f"{indent}Backtracking {num} at ({row}, {col}) [depth {depth}]")
+            board[row][col] = 0
+
+    return False
+
+
+if __name__ == "__main__":
+    # Example Sudoku board (3x3) with some numbers filled in
+    # 0 represents an empty cell
+    # This is a simplified version of a Sudoku board for demonstration purposes
+    # In a real Sudoku, the board would be 9x9 and have more complex rules
+
+    # simplified 3x3 Sudoku board for demonstration, which is not going to call Backtracking
+    board = [
+        [0, 2, 0],
+        [0, 0, 1],
+        [3, 0, 0]
+    ]
+
+    '''
+    Starting to solve the Sudoku...
+    Trying 1 at (0, 0) [depth 0]
+    Board state: [[1, 2, 0], [0, 0, 1], [3, 0, 0]]
+    Trying 3 at (0, 2) [depth 1]
+    Board state: [[1, 2, 3], [0, 0, 1], [3, 0, 0]]
+        Trying 2 at (1, 0) [depth 2]
+        Board state: [[1, 2, 3], [2, 0, 1], [3, 0, 0]]
+        Trying 3 at (1, 1) [depth 3]
+        Board state: [[1, 2, 3], [2, 3, 1], [3, 0, 0]]
+            Trying 1 at (2, 1) [depth 4]
+            Board state: [[1, 2, 3], [2, 3, 1], [3, 1, 0]]
+            Trying 2 at (2, 2) [depth 5]
+            Board state: [[1, 2, 3], [2, 3, 1], [3, 1, 2]]
+                ✔️ Solved at depth 6
+    [1, 2, 3]
+    [2, 3, 1]
+    [3, 1, 2]
+    '''
+
+    # simplified 3x3 Sudoku board for demonstration, which is going to call Backtracking
+    tboard = [
+        [0, 0, 0],
+        [1, 0, 3],
+        [0, 0, 0]
+    ]
+
+    '''
+    Starting to solve the Sudoku...
+    Trying 2 at (0, 0) [depth 0]
+    Board state: [[2, 0, 0], [1, 0, 3], [0, 0, 0]]
+    Trying 1 at (0, 1) [depth 1]
+    Board state: [[2, 1, 0], [1, 0, 3], [0, 0, 0]]
+    Backtracking 1 at (0, 1) [depth 1]
+    Trying 3 at (0, 1) [depth 1]
+    Board state: [[2, 3, 0], [1, 0, 3], [0, 0, 0]]
+        Trying 1 at (0, 2) [depth 2]
+        Board state: [[2, 3, 1], [1, 0, 3], [0, 0, 0]]
+        Trying 2 at (1, 1) [depth 3]
+        Board state: [[2, 3, 1], [1, 2, 3], [0, 0, 0]]
+            Trying 3 at (2, 0) [depth 4]
+            Board state: [[2, 3, 1], [1, 2, 3], [3, 0, 0]]
+            Trying 1 at (2, 1) [depth 5]
+            Board state: [[2, 3, 1], [1, 2, 3], [3, 1, 0]]
+                Trying 2 at (2, 2) [depth 6]
+                Board state: [[2, 3, 1], [1, 2, 3], [3, 1, 2]]
+                ✔️ Solved at depth 7
+    [2, 3, 1]
+    [1, 2, 3]
+    [3, 1, 2]
+    '''
+
+    print("Starting to solve the Sudoku...")
+
+    if solve_sudoku(board):
+        for row in board:
+            print(row)
+    else:
+        print("No solution exists.")