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nQueens.py
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nQueens.py
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from typing import List
import unittest
'''
https://leetcode.com/problems/n-queens/
0(2 ^ N) - TC | 0(N ^ 2) - SC
'''
class Solution:
def solveNQueens(self, n: int) -> List[List[str]]:
col = set()
posDiag = set()
negDiag = set()
res = []
board = [["."] * n for i in range(n)]
def backtrack(r):
if r == n:
copy = ["".join(row) for row in board]
res.append(copy)
return
for c in range(n):
if c in col or (r + c) in posDiag or (r - c) in negDiag:
continue
col.add(c)
posDiag.add(r + c)
negDiag.add(r - c)
board[r][c] = "Q"
backtrack(r + 1)
col.remove(c)
posDiag.remove( r + c)
negDiag.remove(r - c)
board[r][c] = "."
backtrack(0)
return res
class TestSolution(unittest.TestCase):
def test_solveNQueens(self):
self.assertEqual(Solution.solveNQueens(self, 4), [[".Q..","...Q","Q...","..Q."],["..Q.","Q...","...Q",".Q.."]])
self.assertEqual(Solution.solveNQueens(self, 1), [["Q"]])
if __name__ == "__main__":
unittest.main()