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.