package main

import (
    "fmt"
    "strconv"
)
func HpAdd(a string, b string) [] int {
    aslice := make([]int, 0, len(a))
    bslice := make([]int, 0, len(b))
    c := make([]int, 0)

    for i:=len(a)-1; i>=0; i-- {
        ai, _ := strconv.Atoi(string(a[i]))
        aslice = append(aslice, ai)
    }
    for i:=len(b)-1; i>=0; i-- {
        bi, _ :=strconv.Atoi(string(b[i]))
        bslice = append(bslice, bi)
    }

    t := 0
    for i:=0;i<len(aslice) || i <len(bslice); i++ {
        if i <len(aslice) {
            t += aslice[i]  
        }
        if i < len(bslice) {
            t += bslice[i]
        }
        c = append(c, t%10)
        t = t / 10
    }
    if t != 0 {
        c = append(c, t)
    }
    fmt.Println(c)
    return c
}

func HpSub(a string, b string) []int {
    // 123-23
    aslice := make([]int, 0, len(a))
    bslice := make([]int, 0, len(b))
    c := make([]int, 0)

    for i:=len(a)-1; i>=0; i-- {
        ai, _ := strconv.Atoi(string(a[i]))
        aslice = append(aslice, ai)
    }
    for i:=len(b)-1; i>=0; i-- {
        bi, _ :=strconv.Atoi(string(b[i]))
        bslice = append(bslice, bi)
    }
    t := 0
    // 32 211
    // 112 - 23 = 89
    for i:=0; i<len(aslice); i++ {
        t = aslice[i] - t
        if (i < len(bslice)) {
            t = t - bslice[i]
        }
        c = append(c, (t + 10) % 10)
        if (t >= 0) {
            t = 0
        } else {
            t = 1
        }
    }
    for i:=len(c) - 1;len(c) > 1 && c[len(c) - 1] == 0;i-- {
        c = c[:i]
    }
    fmt.Println(c)
    return c
}

func HpMulti(a string, b int) []int {
    aslice := make([]int, 0, len(a))

    c := make([]int, 0)

    for i:=len(a)-1; i>=0; i-- {
        ai, _ := strconv.Atoi(string(a[i]))
        aslice = append(aslice, ai)
    }
    // 12 * 7
    // 21 7
    t := 0
    for i:= 0;i<len(aslice) || t != 0;i++ {
        if (i < len(aslice)) {
            t += aslice[i]*b
        }
        c = append(c, t % 10)
        t /= 10
    }
    fmt.Println(c)
    return c
}

func HpDiv(a string, b int) []int {
    aslice := make([]int, 0, len(a))

    c := make([]int, 0)

    for i:=len(a)-1; i>=0; i-- {
        ai, _ := strconv.Atoi(string(a[i]))
        aslice = append(aslice, ai)
    }
    t := 0
    for i:= len(aslice) - 1;i>=0;i-- {
        t = t * 10 + aslice[i]
        c = append(c, t/b)
        t = t % b
    }

    for i:=0;len(c) > 1 && c[i] == 0;i++ {
        c = c[i+1:]
    }
    fmt.Println(c)
    return c
}

func main() {
    HpAdd("123","923")
    HpSub("1023","934")
    HpMulti("423", 3)
    HpDiv("123",3)
}