392. Is Subsequence

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?

一刷
题解：
判断s是否t的子串，意味着t中delete掉一些字符能构成s(保留字符的相对顺序）
两个字符串都从头开始寻找，当t[index1] == s[index2]的时候，index2++， 如果最终index2 == s.length(), 返回true

class Solution {
    public boolean isSubsequence(String s, String t) {
        if(s.length() == 0) return true;
        int indexS = 0, indexT = 0;
        while(indexT<t.length()){
            if(t.charAt(indexT) == s.charAt(indexS)){
                indexS++;
            }
            indexT++;
            //try to stop in advanxce
            if(indexS == s.length()) return true;
        }
        return false;
    }
}