415. 字符串相加

package main
import "fmt"
func addStrings(num1 string, num2 string) string {
    l1 := len(num1)-1
    l2 := len(num2)-1
    carry :=0
    str :=""
    for l1>=0||l2>=0{
        n1 :=0
        if l1>=0{
            n1 = int(num1[l1]-'0')
            l1--
        }
        n2 :=0
        if l2>=0{
            n2 = int(num2[l2]-'0')
            l2--
        }
        fmt.Println(n2,n1)
        r := n1+n2+carry
        carry= r/10
        str =fmt.Sprintf("%d%s",r%10,str)
    }
    if carry>0{
        str =fmt.Sprintf("1%s",str)
    }
    return str
}
func main() {
    fmt.Println(addStrings("900","211"))
}