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N_queens.py

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+def is_safe(board, row, col):
+    for i in range(row):
+        if board[i] == col or abs(board[i] - col) == abs(i - row):
+            return False
+    return True
+
+def solve_n_queens_first(board, row, n):
+    if row == n:
+        return board[:]  # Return the first solution found
+
+    for col in range(n):
+        if is_safe(board, row, col):
+            board[row] = col
+            result = solve_n_queens_first(board, row + 1, n)
+            if result:  # If solution found, return immediately
+                return result
+            board[row] = -1  # Backtrack
+    return None  # No solution in this path
+
+def print_solution(board, n):
+    for row in range(n):
+        line = ['Q' if i == board[row] else '.' for i in range(n)]
+        print(" ".join(line))
+    print()
+
+def n_queens_one_solution(n):
+    board = [-1] * n
+    solution = solve_n_queens_first(board, 0, n)
+    if solution:
+        print("One valid n-Queens solution:")
+        print_solution(solution, n)
+    else:
+        print("No solution exists.")
+
+# Example: 8-Queens
+n_queens_one_solution(8)