What is LeetCode 647 about?

Count all palindromic substrings in a string using expand around centers—no extra space needed.

How to solve LeetCode palindromic substrings?

Loop every position as center, expand while chars match for odd/even lengths, tally each valid one.

Best visualizer for LeetCode algorithms?

TraceLit steps through code line-by-line; beats static diagrams for dynamic expansions.

LeetCode 647: Palindromic Substrings, the O(n²) Workhorse That Won't Die

Twenty years in tech, and palindromes still trip up FAANG hopefuls. LeetCode 647's expand-around-centers nails it without wasting space—here's why it endures.

theAIcatchup Apr 09, 2026 4 min read

Visual step-by-step trace of expand around centers for LeetCode 647 palindromic substrings

⚡ Key Takeaways

Expand around centers delivers O(n²) time, O(1) space—beats DP on efficiency. 𝕏
Every character is a palindrome center; don't forget singles in counts. 𝕏
Tools like TraceLit make dry runs visual, cutting interview prep debug time. 𝕏

Published by

theAIcatchup

Ship faster. Build smarter.

#LeetCode 647 #TraceLit #algorithm visualization #expand around centers #palindromic substrings #two pointers

Worth sharing?

Get the best Developer Tools stories of the week in your inbox — no noise, no spam.

Originally reported by dev.to

⚡ Key Takeaways

The 60-Second TL;DR

theAIcatchup

Share this article

Worth sharing?

Related Stories

TraceLit: LeetCode's Visual Brain for Pointer Chaos

LeetCode 105 Unlocked: Rebuild Trees from Chaos with Visual Magic

LeetCode 130: Why Reversing the DFS Flood Fill Actually Crushes It

LeetCode 84: Why This Histogram Nightmare Still Humiliates Interviewees

Stay in the loop