Leetcode 392. Is Subsequence

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).

Example 1:Input: s = “abc”, t = “ahbgdc” Output: true

Example 2:Input: s = “axc”, t = “ahbgdc” Output: false

Constraints:

• 0 <= s.length <= 100
• 0 <= t.length <= 104
• s and t consist only of lowercase English letters.

Follow up: Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 109, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?

By using two pointer, it can be easily solved within O(n)

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        s_index = 0
        t_index = 0

        while s_index < len(s) and t_index < len(t):
            if s[s_index] == t[t_index]:
                s_index += 1
            t_index += 1

        return s_index == len(s)