17. Letter Combinations of a Pho

使用回溯算法

func letterCombinations(digits string) []string {
    table := []string{"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}
    ret := []string{}
    if len(digits) > 0 {
        help(&ret, digits, "", 0, table)
    }
    return ret
}

func help(ret *[]string, digits string, cur string, index int, table []string) {
    if index == len(digits) {
        *ret = append(*ret, cur)
        return
    }
    tmp := table[digits[index]-48]
    for _, t := range tmp {
        help(ret, digits, cur+string(t), index+1, table)
    }
}