Is Letter Tile Possibilities easy or hard?

Letter Tile Possibilities is considered a Medium difficulty problem. The recursion itself is straightforward, but handling duplicate characters efficiently and reasoning about permutation counts requires solid understanding of backtracking.

How to solve Letter Tile Possibilities in O(n)?

A true O(n) solution is not possible because the number of possible sequences grows factorially with the number of tiles. The optimal practical solution uses DFS with a frequency map to prune duplicates while exploring permutations, resulting in O(n! * n) complexity.

Letter Tile Possibilities Python or Java solution?

Both Python and Java implementations typically use recursive DFS with a frequency map. The algorithm decrements the character count when choosing a tile, explores deeper sequences, and restores the count during backtracking.

What is the best approach for Letter Tile Possibilities?

The most efficient approach uses DFS with a frequency map. Instead of generating all permutations and removing duplicates, the algorithm tracks how many times each character appears and only explores valid choices. This avoids duplicate work and counts sequences directly during recursion.

What data structure is used in Letter Tile Possibilities?

The optimal solution uses a hash table (frequency map) to store the count of each character and recursion to explore possible sequences. Backtracking manages tile usage, while the frequency structure prevents duplicate permutations.

What is the time complexity of Letter Tile Possibilities?

The worst‑case time complexity is O(n! * n) because the algorithm explores permutations of the tiles and builds sequences of length up to n. The frequency‑map DFS approach still has factorial growth but avoids generating duplicate permutations, making it faster in practice.

Is Letter Tile Possibilities asked at Google, Amazon, or Meta?

Permutation and backtracking problems similar to Letter Tile Possibilities appear in interviews at companies like Google, Amazon, and Meta. The problem tests recursion, counting techniques, and handling duplicates efficiently using frequency maps.

Description Hints 1 Solution Video 13:28

1079. Letter Tile Possibilities

Medium83.5% acceptance5 companies

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.

Asked at 5 companies

Bloomberg

Google Oracle Microsoft Meta

Topics

Hints open one at a time

Hint 1

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

13:28

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution

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1class Solution:
2    def numTilePossibilities(self, tiles: str) -> int:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

"AAB"

Input

"AAABBC"

Input

"V"

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