feat: n-queens

Author: junbinding

back.n-queens.py

@@ -0,0 +1,42 @@
+from typing import List
+
+class Solution:
+    """
+    51. N 皇后
+    https://leetcode-cn.com/problems/n-queens/
+    n 皇后问题研究的是如何将 n 个皇后放置在 n×n 的棋盘上，并且使皇后彼此之间不能相互攻击。
+    """
+    def solveNQueens(self, n: int) -> List[List[str]]:
+        pie = set()
+        na = set()
+        shu = set()
+        res = []
+        tmp = []
+        def dfs(row):
+            if row == n:
+                res.append(tmp[:])
+                return
+
+            for c in range(n):
+                if c in shu or c + row in pie or row - c in na:
+                    continue
+
+                shu.add(c)
+                pie.add(row + c)
+                na.add(row - c)
+                l = ['.' for i in range(n)]
+                l[c] = 'Q'
+                tmp.append(''.join(l))
+                dfs(row + 1)
+                tmp.pop()
+                shu.remove(c)
+                pie.remove(row + c)
+                na.remove(row - c)
+
+
+        dfs(0)
+        return res
+
+
+so = Solution()
+print(so.solveNQueens(3))