Understanding Subsequence Validation in Strings
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Chapter 1: Introduction to the Problem
In this section, I will discuss the subsequence problem, which I chose to tackle on the fourth day of the Leetcode 75-day challenge. Before diving into the solution, I assume readers are familiar with the two-pointer technique. If you need a refresher, you can view a helpful YouTube video on this approach here:
The task is straightforward: Given two strings, s and t, determine whether s is a subsequence of t. A subsequence is formed by deleting some characters (possibly none) from the original string while preserving the order of the remaining characters. For instance, "ace" is a subsequence of "abcde," whereas "aec" is not.
Example 1:
- Input: s = "abc", t = "ahbgdc"
- Output: true
Example 2:
- Input: s = "axc", t = "ahbgdc"
- Output: false
Chapter 2: Solution Breakdown
The solution to this problem is relatively simple, as outlined below:
- Base Cases:
- If s is empty, it is considered a subsequence of any string t, hence the function returns true.
- Conversely, if t is empty and s is not, then s cannot be a subsequence of t, resulting in a return value of false.
- Iterative Comparison:
- Two pointers, sStartIndex and tStartIndex, are initialized at the start of both strings.
- The algorithm iterates through t until reaching its end or finding all characters of s.
- If characters at the current indices of s and t match, the pointer for s advances. Regardless, the pointer for t moves forward.
- After the loop concludes, if sStartIndex has traversed the entirety of s, it indicates that all characters have been found in t, prompting a return of true. If not, false is returned.
- Final Return:
- The function returns true if sStartIndex equals the length of s, confirming that all characters of s are present in t.
If you find this solution helpful or have suggestions for improvement, feel free to leave a comment or give it a clap!
The second video provides further insights into the longest ideal subsequence problem, enhancing your understanding of this topic.