Merge sort recursive

mergesort.go

package main
import (
    "fmt"
    "bufio"
    "os"
)

//see Cracking Code Interview
//practice merge sort (recursive; next try iterative...)
//input is n items on line 1, then space separated values on line 2
func main() {
    var n int;
    var v int;
    scanner := bufio.NewReader(os.Stdin)
    _, err := fmt.Fscanf(scanner, "%d\n", &n)
    if err != nil {
        panic(err.Error())
    }
    a := make([]int, n)
    tmp := make([]int, n)
    for i :=0; i <n-1; i++ {
        _, err = fmt.Fscanf(scanner, "%d ", &v)
        a[i] = v
    }
    _, err = fmt.Fscanf(scanner, "%d\n", &v)
    a[n-1] = v

    mergesort(a, tmp, 0, n-1)
    fmt.Printf("%v\n", a)
}

func mergesort(a []int, tmp []int, leftStart int, rightEnd int) {
    if leftStart >= rightEnd {
        return
    }
    mid := leftStart + (rightEnd-leftStart)/2

    mergesort(a, tmp, leftStart, mid)
    mergesort(a, tmp, mid+1, rightEnd)
    mergeHalves(a, tmp, leftStart, rightEnd)
}

func mergeHalves(a []int, tmp []int, leftStart int, rightEnd int) {
    leftEnd := leftStart + (rightEnd-leftStart)/2
    left := leftStart
    right := leftEnd +1
    i := leftStart

    for ; left <= leftEnd && right <= rightEnd; {
        if a[left] <= a[right] {
            tmp[i] = a[left]
            left++
        } else {
            tmp[i] = a[right]
            right++
        }
        i++
    }
    //copy remainder from left (either lt or rt and not both, notice the start index of destination)
////        copy(tmp[i:], a[left:(leftEnd-left +1)])
    h := i
    for j := left; j <= leftEnd; j++ {
        tmp[h] = a[j]
        h++
    }
    //copy remainder from right (either lt or rt and not both, notice the start index of destination)
////        copy(tmp[i:], a[right:(rightEnd-right +1)])
    h = i
    for j := right; j <= rightEnd; j++ {
        tmp[h] = a[j]
        h++
    }

    //copy tmp over arr
////    copy(a[leftStart:], tmp[leftStart:size])
    for j := leftStart; j <= rightEnd; j++ {
        a[j] = tmp[j]
    }
}