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Given a string s and a string t, check if s is subsequence of t. You may assume that there is only lower case English letters in both s and t. t is potentially a very long (length ~= 500,000) string, and s is a short string (<=100). A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, “ace”  is a subsequence of “abcde”  while “aec”  is not). **Example 1:**s = “abc” , t = “ahbgdc”

Return true . **Example 2:**s = “axc” , t = “ahbgdc”

Return false . **Follow up:**If there are lots of incoming S, say S1, S2, … , Sk where k >= 1B, and you want to check one by one to see if T has its subsequence. In this scenario, how would you change your code?

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 // use two pointers
    // https://discuss.leetcode.com/topic/57147/straight-forward-java-simple-solution
    public boolean isSubsequence(String s, String t) {
        if ( s.length() == 0) return true;
        
        int i = 0, j = 0;   // index of s, t
        while (j < t.length()) {
             if (s.charAt(i)  == t.charAt(j) ) {
                i++;
            }
            if (i == s.length()) return true;
            j++;
        }
        return false;
    }