Add Connect Four game implementation

connect_four.py

@@ -0,0 +1,170 @@
+#!/usr/bin/env python3
+"""
+Connect Four – a simple console implementation for one or two players.
+
+The game uses a 6x7 board. Players take turns dropping a disc into one of the
+seven columns. The disc occupies the lowest available row in that column.
+The first player to connect four of their discs horizontally, vertically,
+or diagonally wins. If the board fills without a winner, the game ends in a
+draw.
+
+Usage:
+    python connect_four.py
+
+The program will prompt for the number of players (1 or 2). In single‑player
+mode the second player is a very simple AI that chooses the first available
+column. Feel free to replace the AI logic with something more sophisticated.
+"""
+
+from __future__ import annotations
+import sys
+import random
+from typing import List, Tuple
+
+ROWS: int = 6
+COLUMNS: int = 7
+EMPTY: str = " "
+PLAYER_SYMBOLS: Tuple[str, str] = ("X", "O")
+
+
+def create_board() -> List[List[str]]:
+    """Return a new empty board."""
+    return [[EMPTY for _ in range(COLUMNS)] for _ in range(ROWS)]
+
+
+def print_board(board: List[List[str]]) -> None:
+    """Print the board to the console."""
+    print("\n" + "  ".join(str(i + 1) for i in range(COLUMNS)))
+    for row in board:
+        print("|" + "|".join(row) + "|")
+    print("-" * (COLUMNS * 2 + 1))
+
+
+def is_valid_move(board: List[List[str]], col: int) -> bool:
+    """Return True if a disc can be dropped into the given column."""
+    return board[0][col] == EMPTY
+
+
+def make_move(board: List[List[str]], col: int, symbol: str) -> None:
+    """Drop a disc into the given column."""
+    for row in reversed(range(ROWS)):
+        if board[row][col] == EMPTY:
+            board[row][col] = symbol
+            break
+
+
+def check_direction(
+    board: List[List[str]],
+    start_row: int,
+    start_col: int,
+    delta_row: int,
+    delta_col: int,
+    symbol: str,
+) -> bool:
+    """Check a line of four in a specific direction."""
+    count = 0
+    row, col = start_row, start_col
+    while 0 <= row < ROWS and 0 <= col < COLUMNS:
+        if board[row][col] == symbol:
+            count += 1
+            if count == 4:
+                return True
+        else:
+            count = 0
+        row += delta_row
+        col += delta_col
+    return False
+
+
+def check_win(board: List[List[str]], symbol: str) -> bool:
+    """Return True if the given symbol has a connect four."""
+    # Horizontal
+    for r in range(ROWS):
+        if check_direction(board, r, 0, 0, 1, symbol):
+            return True
+    # Vertical
+    for c in range(COLUMNS):
+        if check_direction(board, 0, c, 1, 0, symbol):
+            return True
+    # Diagonal /
+    for r in range(ROWS - 3):
+        for c in range(COLUMNS - 3):
+            if check_direction(board, r, c, 1, 1, symbol):
+                return True
+    # Diagonal \
+    for r in range(3, ROWS):
+        for c in range(COLUMNS - 3):
+            if check_direction(board, r, c, -1, 1, symbol):
+                return True
+    return False
+
+
+def board_full(board: List[List[str]]) -> bool:
+    """Return True if the board has no empty cells."""
+    return all(cell != EMPTY for cell in board[0])
+
+
+def get_player_move(board: List[List[str]], player_num: int) -> int:
+    """Prompt the human player for a column."""
+    while True:
+        try:
+            col = int(input(f"Player {player_num} ({PLAYER_SYMBOLS[player_num - 1]}), choose column (1-{COLUMNS}): ")) - 1
+            if 0 <= col < COLUMNS and is_valid_move(board, col):
+                return col
+            print(f"Column {col + 1} is full or out of range. Try again.")
+        except ValueError:
+            print("Invalid input. Enter a number.")
+
+
+def get_ai_move(board: List[List[str]]) -> int:
+    """Very simple AI: choose the first available column."""
+    for col in range(COLUMNS):
+        if is_valid_move(board, col):
+            return col
+    # Should never reach here if called correctly
+    raise RuntimeError("No valid moves for AI")
+
+
+def main() -> None:
+    print("Welcome to Connect Four!")
+    while True:
+        try:
+            num_players = int(input("Enter number of players (1 or 2): "))
+            if num_players in (1, 2):
+                break
+            print("Please enter 1 or 2.")
+        except ValueError:
+            print("Invalid input. Enter a number.")
+
+    board = create_board()
+    current_player = 1
+    while True:
+        print_board(board)
+        if num_players == 1 and current_player == 2:
+            col = get_ai_move(board)
+            print(f"AI chooses column {col + 1}")
+        else:
+            col = get_player_move(board, current_player)
+
+        make_move(board, col, PLAYER_SYMBOLS[current_player - 1])
+
+        if check_win(board, PLAYER_SYMBOLS[current_player - 1]):
+            print_board(board)
+            if num_players == 1 and current_player == 2:
+                print("AI wins! Better luck next time.")
+            else:
+                print(f"Player {current_player} ({PLAYER_SYMBOLS[current_player - 1]}) wins!")
+            break
+
+        if board_full(board):
+            print_board(board)
+            print("It's a draw!")
+            break
+
+        current_player = 2 if current_player == 1 else 1
+
+    print("Thanks for playing!")
+
+
+if __name__ == "__main__":
+    main()