递归和回溯_leetcode52

class Solution(object):
    def totalNQueens(self, n):
        """
        :type n: int
        :rtype:
        """
        self.col = [False for i in range(n)]
        self.diaS = [False for i in range(2 * n - 1)]
        self.diaN = [False for i in range(2 * n - 1)]

        ans = []
        self.res = 0

        self.putQueen(n, 0, ans)

        print self.res



        # 尝试在一个n皇后的问题中，摆放第index行皇后的位置

    def putQueen(self, n, index, ans):
        if index == n:
            self.res += 1
            # self.res.append(ans[0:])

            return

        # 尝试将第index行的皇后摆放在第i列
        for i in range(n):
            if not self.col[i] and not self.diaS[index + i] and not self.diaN[index - i + n - 1]:
                ans.append(i)

                self.col[i] = True
                self.diaS[index + i] = True
                self.diaN[index - i + n - 1] = True

                self.putQueen(n, index + 1, ans)

                ans.pop()
                self.col[i] = False
                self.diaS[index + i] = False
                self.diaN[index - i + n - 1] = False

        return