cmd/aefix/fix.go
func matchLen(x, y string) int {
	i := 0
	for i < len(x) && i < len(y) && x[i] == y[i] {
		i++
	}
	return i
}
func matchLen(x, y string) int {
	i := 0
	for i < len(x) && i < len(y) && x[i] == y[i] {
		i++
	}
	return i
}
// matchLen returns the length of the longest prefix shared by x and y.