is-subsequence

public class Solution {
    public boolean isSubsequence(String s, String t) {
        int idx = 0;
        for (int i=0; i<t.length()&&idx<s.length(); i++) {
            if (s.charAt(idx) == t.charAt(i)) {
                idx++;
            }
        }
        return idx == s.length();
    }
}