import copy
class Solution:
    """
    Get all distinct N-Queen solutions
    @param n: The number of queens
    @return: All distinct solutions
    """

    def solveNQueens(self, n):
        # write your code here
        self.n = n
        self.x = [0 for i in range(n)]
        self.ans = []
        self.backtrak(0)
        ans_sum = len(self.ans)
        res = [[['.' for i in range(n)] for i in range(n)] for i in range(ans_sum)]

        for i in range(ans_sum):
            for j in range(self.n):
                res[i][j][self.ans[i][j]] = 'Q'

        r_res = []
        for res_list in res:
            tmp_l = []
            for i in range(n):
                tmp_s = ''
                for j in range(n):
                    tmp_s += res_list[i][j]
                tmp_l.append(tmp_s)
            r_res.append(tmp_l)

        return r_res

    def backtrak(self, t):
        if t == self.n:
            self.ans.append(copy.copy(self.x))
        else:
            for i in range(self.n):
                self.x[t] = i
                if self.place(t):
                    self.backtrak(t+1)

    def place(self, k):
        for j in range(k):
            if abs(self.x[k]-self.x[j]) == abs(k-j) or self.x[j] == self.x[k]:
                return False
        return True

if __name__ == '__main__':
    s = Solution()
    print s.solveNQueens(4)