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:
    def isSubsequence(self, s, t):
        pointer1 = 0
        pointer2 = 0

        while pointer1 < len(s) and pointer2 < len(t):
            if s[pointer1] == t[pointer2]:
                pointer1 += 1

            pointer2 += 1

        if pointer1 == len(s):
            return True

        return False