README.md

1079. Letter Tile Possibilities

You have n 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 using the letters printed on those tiles.

Example 1:

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

Example 2:

Input: tiles = "AAABBC"
Output: 188

Example 3:

Input: tiles = "V"
Output: 1

Constraints:

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

Solutions (Python)

1. Solution

class Solution:
    def numTilePossibilities(self, tiles: str) -> int:
        return len(self.dfs(tiles))

    def dfs(self, tiles: str) -> Set[str]:
        ret = set()

        for i in range(len(tiles)):
            ret.add(tiles[i])
            for s in self.dfs(tiles[:i] + tiles[i + 1:]):
                ret.add(s)
                ret.add(tiles[i] + s)

        return ret