class Solution {
    public boolean isSubsequence(String s, String t) {
        if (s == null || s.length() == 0) return true;
        int i = 0;
        int j = 0;

        while (i < s.length() && j < t.length()) {
            if (s.charAt(i) == t.charAt(j)) {
                i++;

                if (i == s.length()) return true;
            }

            j++;
        }

        return false;
    }
}