golang算法--leetcode17

Letter Combinations of a Phone Number

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

package main

import (
    "fmt"
)

func letterCombinations(digits string) []string {
    if (len(digits)) == 0 {
        return nil
    }
    AllDigits := map[byte][]string{
        '0': {" "},
        '1': {""},
        '2': {"a", "b", "c"},
        '3': {"d", "e", "f"},
        '4': {"g", "h", "i"},
        '5': {"j", "k", "l"},
        '6': {"m", "n", "o"},
        '7': {"p", "q", "r", "s"},
        '8': {"t", "u", "v"},
        '9': {"w", "x", "y", "z"},
    }
    var cur string
    answer := make([]string, 0)
    dfs(digits, AllDigits, 0, cur, &answer)
    fmt.Println(answer)
    return answer
}
func dfs(digits string, AllDigits map[byte][]string, l int, cur string, answer *[]string) {
    if l == len(digits) {
        *answer = append(*answer, cur)
        return
    }
    for _, n := range AllDigits[byte(digits[l])] {
        cur = cur + n
        dfs(digits, AllDigits, l+1, cur, answer)
        cur = cur[:int(len(cur)-1)]
    }
}