试题：
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?
Credits:
Special thanks to @pbrother for adding this problem and creating all test cases.
代码：
遍历s，同时又相同时t位置+1.
class Solution {
public boolean isSubsequence(String s, String t) {
if(s==null || s.length()==0) return true;
if(t==null || t.length()==0) return false;
int si=0;
for(int i=0; i<t.length(); i++){
if(t.charAt(i)==s.charAt(si)){
si++;
}
if(si==s.length()) return true;
}
return false;
}
}