Create 0051_N-Queen_1.py

LeetCode/0051_N-Queen_1.py

@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+"""
+Created on Wed Oct  7 20:51:57 2020
+
+@author: anjalisingh
+"""
+
+class Solution(object):
+    def solveNQueens(self, n):
+        # i is column index
+        # left: left diagonal: \ level-i
+        # right: right diagonal: / level+i
+        self.col = [0]*n # not occupied column
+        self.left = [0]*(2*n-1) # number of left diagonal
+        self.right = [0]*(2*n-1)
+        board = [['.' for x in range(n)] for y in range(n)]
+        self.resultBoard = []
+        self.backTrack(n, 0, board)
+        return self.resultBoard
+
+    def backTrack(self, n, level, board):
+        if level == n: # finish
+            res = []
+            for i in range(n):
+                res.append(''.join(board[i]))
+            self.resultBoard.append(res)
+            return
+        for i in range(n): # iterate every column
+            # if col, left, right are all not accupied, put a queue here
+            if not self.col[i] and not self.left[level-i] and not self.right[level+i]:
+                board[level][i] = 'Q'
+                self.col[i] = 1
+                self.left[level-i] = 1
+                self.right[level+i] = 1 # choose
+                self.backTrack(n, level+1, board) # explore
+                board[level][i] = '.' # un choose
+                self.col[i] = 0
+                self.left[level-i] = 0
+                self.right[level+i] = 0
+
+# Queen  = Solution()
+# print(Queen.solveNQueens(4))