is_subsequence.py

"""
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?
"""

class Solution:

    """
	cost: 104 ms > 76.41
	memory: >26.67
	https://leetcode.com/submissions/detail/315409362/
        tc: O(n)
	sc: O(1)
    """
    def isSubsequence(self, s: str, t: str) -> bool:
        if not s:
            return True

        index = 0

        for tc in t:
            if s[index] == tc:
                index += 1
                if index == len(s):
                    return True

        return False