1079. Letter Tile Possibilities
https://leetcode.com/problems/letter-tile-possibilities/description/ 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. ------------