392. Is Subsequence

Total Accepted: 9572
Total Submissions: 21748
Difficulty: Medium

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?

 // use two pointers
    // 
    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;
    }