DSA · Two Pointers · #91

Is Subsequence

Module 69 · difficulty 2/5·⏱ 30:00starts on first keystroke

Given two strings `s` and `t`, return `true` if `s` is a subsequence of `t`, and `false` otherwise. A subsequence of a string is a new string formed from the original by deleting some (possibly zero) characters without changing the relative order of the remaining characters. For example, `"ace"` is a subsequence of `"abcde"`. Implement `function isSubsequence(s, t)` returning a boolean.

Examples

s = "abc", t = "ahbgdc" → true — a, b, c appear in order within t.
s = "axc", t = "ahbgdc" → false — x never appears, so s cannot be a subsequence.
s = "", t = "ahbgdc" → true — The empty string is a subsequence of any string.

Constraints

· 0 <= s.length <= 100
· 0 <= t.length <= 10^4
· s and t consist only of lowercase English letters.

Session phases

A · Clarify

B · Approach

C · Complexity

D · Edges

E · Code

F · Tradeoff

G · Score

Phase A — Clarify

Ask questions about input bounds, types, and edge constraints.

Ask the coach clarifying questions about the problem.

When you've covered this phase, advance to the next.