class Solution { public boolean isSubsequence(String s, String t) { if(s==null||s.length()==0)return true; if(t==null||t.length()==0)return false; int len = s.length(); int i = 0; int j = 0; while (i < len && j < t.length()) { if(s.charAt(i)==t.charAt(j))i++; if (i == s.length()) { return true; } j++; } return false; } }