reverse.go

package main

func main() {
	arr := []int{5, 4, 3, 2, 1}
	l := len(arr)
	for i, e := range arr[:l/2] {
		j := l - 1 - i
		arr[i] = arr[j]
		arr[j] = e
	}
	for i, e := range arr {
		if e != i+1 {
			panic("oops")
		}
	}
}