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?

Credits:
Special thanks to @pbrother for adding this problem and creating all test cases.

判断子串s是否为主串t的子序列

C++：

class Solution {
public:
    bool isSubsequence(string s, string t) {
        if (s.size() == 0){
            return true ;
        }
        int j = 0 ;
        char temp = s[j] ;
        for(char c : t){
            if (c == temp){
                if (j == s.size()-1){
                    return true ;
                }
                temp = s[++j] ;
            }
        }
        return false ;
    }
};