題目：

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:

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?

 題目描述：

      判斷s是否為t的子序列

具體解題思路及程式碼如下：

package Leetcode_Github;

public class GreedyThought_IsSubsequence_392_1112 {
    public boolean IsSubsequence(String s, String t) {
        
        //記錄s中字元在t中出現的位置
        int index = -1;

        //從頭向後遍歷字串t
        for (char c : s.toCharArray()) {
            index = t.indexOf(c, index + 1);
            if (index == -1) {
                return false;
            }
        }
        return true;
    }
}