题目链接

思路

一个一个遍历就好了，不难。

代码

class Solution {
    fun letterCombinations(digits: String): List<String> {
        if (digits.isEmpty()) return emptyList()
        val map = mapOf(
            '2' to arrayOf('a', 'b', 'c'),
            '3' to arrayOf('d', 'e', 'f'),
            '4' to arrayOf('g', 'h', 'i'),
            '5' to arrayOf('j', 'k', 'l'),
            '6' to arrayOf('m', 'n', 'o'),
            '7' to arrayOf('p', 'q', 'r', 's'),
            '8' to arrayOf('t', 'u', 'v'),
            '9' to arrayOf('w', 'x', 'y', 'z')
        )
        var result = mutableListOf("")
        var index = 0
        while (index < digits.length) {
            var nowList = mutableListOf<String>()
            val char = digits[index]
            result.forEach{str ->
                map[char]?.forEach {c ->
                    nowList.add(str + c)
                }
            }
            index++
            result = nowList
        }
        return result
    }
}