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.

思路：DFS

from collections import Counter
class Solution(object):
    def numTilePossibilities(self, tiles):
        """
        :type tiles: str
        :rtype: int
        """
        res=set()
        p=[]
        def dfs():
            res.add(''.join(p))
            if not ss: return
            for s in d:
                if d[s]==0: continue
                p.append(s)
                d[s]-=1
                dfs()
                d[s]+=1
                p.pop()
                
        ss=[s for s in tiles]
        d=Counter(ss)
        dfs()
        return len(res)-1