Time: 54 ms (54.21%), Space: 17.1 MB (43.25%) - LeetHub

Author: RootProgrammer

Diff for: 0051-n-queens/0051-n-queens.py

@@ -0,0 +1,38 @@
+class Solution:
+    def solveNQueens(self, n: int) -> List[List[str]]:
+        # file=column, rank=row, empty/non-empty cell=square
+        columns = set()
+        upward_diagonal = set() # row+column
+        downward_diagonal = set() # row-column
+        board = [["."] * n for square in range(n)]
+        result = []
+
+        def backtrack(row):
+            # Base Case
+            if row == n:
+                board_snap = ["".join(row) for row in board]
+                result.append(board_snap)
+                return
+
+            # Recursive Case
+            for column in range(n):
+                if column in columns or (row + column) in upward_diagonal or (row - column) in downward_diagonal:
+                    continue
+
+                # update for recursive call
+                columns.add(column)
+                upward_diagonal.add(row + column)
+                downward_diagonal.add(row - column)
+                board[row][column] = "Q"
+
+                backtrack(row + 1)
+
+                # clear before next recursion
+                columns.remove(column)
+                upward_diagonal.remove(row + column)
+                downward_diagonal.remove(row - column)
+                board[row][column] = "."
+
+        backtrack(0)
+
+        return result