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
}
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.
matchLen returns the length of the longest prefix shared by x and y .