golang数组-----寻找数组中缺失的整数方法

package main
import (
	"errors"
	"fmt"
)
func getMissingElement(arr []int) int {
	var sumA, sumB int
	if arr == nil || len(arr) <= 0 {
		errors.New("空数组")
	}
	for k, v := range arr {
		sumA += v
		sumB += k
	}
	sumB = sumB + len(arr)*2 + 1
	return sumB - sumA
}
func main() {
	var arr []int
	arr = []int{1, 3, 2, 6, 5, 7, 8}
	fmt.Println(getMissingElement(arr))
}