这一题的写法是模仿discussion中的Java的。总的来说分为以下几个部分，初始化board的时候把所有的点的值都初始化为'.'，在遍历的时候按照列索引，判断列中行坐标的点是否可以放置，直到列索引达到最后，这样可以确定一种答案
class Solution(object):
def solveNQueens(self, n):
"""
:type n: int
:rtype: List[List[str]]
"""
board = [['.' for i in range(n)] for i in range(n)]
res = []
self.dfs(0, board, res)
return res
def dfs(self, curcol, board, res):
if curcol == len(board):
res.append(self.construct(board))
return
for i in range(len(board)):
if self.check(board, i, curcol):
board[i][curcol] = 'Q'
self.dfs(curcol+1, board, res)
board[i][curcol] = '.'
def check(self, board, x, y):
for i in range(len(board)):
for j in range(y):
if board[i][j] == 'Q' and ((x+j == y+i) or (x+y == i+j) or (x==i)):
return False
return True
def construct(self, board):
res = []
for i in range(len(board)):
s = ''
for j in range(len(board)):
s += board[i][j]
res.append(s)
return res
