Is a Subsequence

L3 Easy Two Pointers

Concept

Two pointers can walk two strings at once. To check subsequence, match characters greedily: advance the needle pointer only on a match, always advance the haystack pointer.

Given strings s and t, return true if s is a subsequence of t — that is, you can delete some characters from t (possibly zero) and be left with exactly s — otherwise return false.

Examples

▸ s = "abc", t = "ahbgdc"

→ true

▸ s = "axc", t = "ahbgdc"

→ false

▸ s = "", t = "anything"

→ true

Progressive Hints

Hint 1 · Nudge

Try to match t against s in order, never stepping backwards.

Hint 2 · Plan

Keep an index into s. Loop over the characters of t; each time a character matches the character of s at that index, advance the index. If the index reaches the end of s, return true.

Hint 3 · Approach

i = 0. For each c in t: if i is smaller than s's length and c == s[i], then i = i + 1. Return true exactly when i reached the end of s.

Output

// Run your code to see the output here.