Add N-Queens backtracking solution

n_queens/n_queens.py

@@ -0,0 +1,42 @@
+def is_safe(board, row, col, n):
+    for i in range(row):
+        if board[i] == col:
+            return False
+
+        if abs(board[i] - col) == abs(i - row):
+            return False
+
+    return True
+
+
+def solve(board, row, n):
+    if row == n:
+        return True
+
+    for col in range(n):
+        if is_safe(board, row, col, n):
+            board[row] = col
+
+            if solve(board, row + 1, n):
+                return True
+
+            board[row] = -1
+
+    return False
+
+
+def print_board(board, n):
+    for row in range(n):
+        for col in range(n):
+            print("Q" if board[row] == col else ".", end=" ")
+        print()
+
+
+n = int(input("Enter the number of queens: "))
+
+board = [-1] * n
+
+if solve(board, 0, n):
+    print_board(board, n)
+else:
+    print("No solution exists.")