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.

Runtime: 120 ms, faster than 12.75% of C++ online submissions for Is Subsequence.
Memory Usage: 14.8 MB, less than 100.00% of C++ online submissions for Is Subsequence.

class Solution {
public:
    bool isSubsequence(string s, string t) {
        if (s.length() > t.length()) {
            return false;
        }
        if (s.empty() || t.empty()) {
            return true;
        }
        int pos = 0;
        for (int i = 0; i < t.length(); i++) {
            if (s[pos] == t[i]) {
                pos++;
            }
            if (pos == s.length()) {
                return true;
            }
        }
        return false;
    }
};