nqueens solution

0x05-nqueens/0-nqueens.py

@@ -0,0 +1,66 @@
+#!/usr/bin/python3
+"""N queens puzzle"""
+import sys
+
+
+def print_solutions(solutions):
+    """Prints the coordinates of the queens"""
+    for solution in solutions:
+        print(solution)
+
+
+def is_safe(board, row, col):
+    """Checks if a queen can be placed on board at the given position"""
+    n = len(board)
+
+    for i in range(row):
+        if board[i][col] == 1 or \
+           (0 <= col - row + i < n and board[i][col - row + i] == 1) or \
+           (0 <= col + row - i < n and board[i][col + row - i] == 1):
+            return False
+
+    return True
+
+
+def backtrack(board, row, solutions):
+    """Solves the N queens problem using Backtracking"""
+    n = len(board)
+
+    if row == n:
+        queens = [[i, j] for i in range(n)
+                  for j in range(n) if board[i][j] == 1]
+        solutions.append(queens)
+        return
+
+    for col in range(n):
+        if is_safe(board, row, col):
+            board[row][col] = 1
+            backtrack(board, row + 1, solutions)
+            board[row][col] = 0
+
+
+def solve_nqueens(n):
+    """Solves the N queens problem"""
+    solutions = []
+    board = [[0 for _ in range(n)] for _ in range(n)]
+    backtrack(board, 0, solutions)
+    return solutions
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        print("Usage: nqueens N")
+        sys.exit(1)
+
+    try:
+        N = int(sys.argv[1])
+    except ValueError:
+        print("N must be a number")
+        sys.exit(1)
+
+    if N < 4:
+        print("N must be at least 4")
+        sys.exit(1)
+
+    solutions = solve_nqueens(N)
+    print_solutions(solutions)

0x05-nqueens/README.md

@@ -12,7 +12,7 @@ Write a program that solves the N queens problem.
     * If N is smaller than `4`, print `N must be at least 4`, followed by a new line, and exit with the status `1`
 * The program should print every possible solution to the problem
     * One solution per line
-    * Format: see example
+    * Format: see [example](#example)
     * You don’t have to print the solutions in a specific order
 * You are only allowed to import the `sys` module