【leetcode】1079. Letter Tile Possibilities

题目如下：

You have a set of tiles, where each tile has one letter tiles[i]printed on it.  Return the number of possible non-empty sequences of letters you can make.

Example 1:

Input: "AAB"
Output: 8
Explanation: The possible sequences are "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA".

Example 2:

Input: "AAABBC"
Output: 188

Note:

1. 1 <= tiles.length <= 7
2. tiles consists of uppercase English letters.

解题思路：tiles的最大长度是7，那么理论上最多有7!种组合，这个数量非常小，可以全排列所有的的可能性然后过滤重复的数据。

代码如下：

class Solution(object):
    def numTilePossibilities(self, tiles):
        """
        :type tiles: str
        :rtype: int
        """
        import itertools
        l = range(len(tiles))
        dic = {}
        for i in range(1,len(l) + 1):
            for j in itertools.permutations(l, i):
                v = ''
                for k in j:
                    v += tiles[k]
                if v not in dic:dic[v] = 1
        return len(dic)