Is Subsequence

Problem Statement

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

A subsequence of a string is a new string formed from the original string by deleting some (possibly none) characters without changing the order of the remaining characters. For example, "ace" is a subsequence of "abcde", but "aec" is not.

Examples

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 <= 10^4
• s and t consist only of lowercase English letters.

Follow Up

Suppose there are a large number of incoming strings s1, s2, ..., sk where k >= 10^9, and you want to check for each if t contains it as a subsequence. How would you optimize your approach for this scenario?

Code Template

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        # Your code here
        pass

Solutions

• Solution 1: This approach uses two pointers to check if s is a subsequence of t. It has a time complexity of O(n) and a space complexity of O(1).
• Solution 2: This approach preprocesses t to allow for efficient checking of multiple s strings using binary search. It has a preprocessing time complexity of O(n) and each query takes O(m log n), where m is the length of s and n is the length of t. The space complexity is O(n).

Back to Problem List

Back to Categories