17. 电话号码的字母组合

package main
import (
    "fmt"
)
func letterCombinations(digits string) []string {
    if digits == "" || len(digits) == 0 {
        return nil
    }
    nums :=[]string{"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"}
    list :=[]string{""}// 默认为空字符
    for i:=0;i<len(digits);i++{
        s :=nums[digits[i]-'0']
        size :=len(list)
        for j:=0;j<size;j++{
            first := list[0]
            list = list[1:]
            for k:=0;k<len(s);k++{
                list = append(list,first+string(s[k]))
            }
        }
    }
    return list
}
func main() {
    fmt.Println(letterCombinations("23"))
}

func letterCombinations(digits string) []string {
    if digits == "" || len(digits) == 0 {
        return nil
    }
    nums :=[]string{"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"}
    var res []string
    res = append(res,"")
    for i :=range digits{
         s := nums[digits[i]-'0']
         var temp []string
         for i:=0;i<len(s);i++{
             for j:=0;j<len(res);j++{
                 temp = append(temp,res[j]+string(s[i]))

            }
         }
         res = temp
    }
    return res
}


func main() {
    fmt.Println(letterCombinations("234"))
}