letter_tile_possibilities

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1079. Letter Tile Possibilities (Medium)

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.

Related Topics

[Backtracking]

Hints

Hint 1

Try to build the string with a backtracking DFS by considering what you can put in every position.