LeetCode in Kotlin

1079. Letter Tile Possibilities

Medium

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.

Solution

class Solution {
    private var count = 0

    fun numTilePossibilities(tiles: String): Int {
        count = 0
        val chars = tiles.toCharArray()
        chars.sort()
        val visited = BooleanArray(chars.size)
        dfs(chars, 0, visited)
        return count
    }

    private fun dfs(chars: CharArray, length: Int, visited: BooleanArray) {
        if (length == chars.size) {
            return
        }
        for (i in chars.indices) {
            if (visited[i] || i - 1 >= 0 && chars[i] == chars[i - 1] && !visited[i - 1]) {
                continue
            }
            count++
            visited[i] = true
            dfs(chars, length + 1, visited)
            visited[i] = false
        }
    }
}

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