static int f(String s1, String s2){ if (s1.length() > s2.length()) return -1; char[] c1 = s1.toCharArray(); char[] c2 = s2.toCharArray(); int index = 0; for (int i = 0; i < c2.length; i++) { if (c2[i] == c1[index] && ++index == c1.length) return i; } return -1; }