Valid Palindrome

L3 Easy Two Pointers

Concept

When junk characters are sprinkled throughout, two pointers still work — they simply skip over anything that is not a letter or digit.

A phrase reads the same forwards and backwards once you ignore anything that is not a letter or digit and ignore letter case. Given s, return true if it qualifies, and false otherwise.

Examples

▸ s = "Was it a car or a cat I saw?"

→ true

▸ s = "Hello, world!"

→ false

▸ s = "12321"

→ true

Progressive Hints

Hint 1 · Nudge

Letters and digits are the only things that matter, and case goes quiet.

Hint 2 · Plan

Put one pointer at the start and one at the end. While they haven't crossed, skip any character that isn't a letter or digit on each side, compare the two you stop on, and return false if they differ. Move both inward.

Hint 3 · Approach

left = 0, right = last index. While left < right: skip non-alphanumeric characters on each side, compare the lowercased letters, return false if they differ, then move both inward. Return true.

Output

// Run your code to see the output here.