LeetCode 647 solution explained?

Expand around 2n-1 centers, odd and even. O(n²) time, counts all layers per center.

How to count palindromic substrings efficiently?

Use two-pointer expansion from centers. Avoid DP for space. Code's 15 lines.

Best visualizer for LeetCode palindromes?

TraceLit steps code visually. Free, interactive. Pairs with manual paper traces.

LeetCode 647's Expand-Around-Centers: Tracing Palindromes That Unravel Strings

LeetCode 647 hits you with 'babad' and asks: how many palindromic substrings lurk inside? The expand-around-centers trick counts them all in O(n²), no extra space wasted.

theAIcatchup Apr 09, 2026 4 min read

Step-by-step visual trace of expand around centers algorithm for LeetCode 647 palindromic substrings

⚡ Key Takeaways

Expand-around-centers counts all palindromic substrings in O(n²) time with O(1) space by treating every position as a potential center. 𝕏
Each expansion layer adds one palindrome, uniquely attributing them to centers to avoid overlaps. 𝕏
Master this for interviews — it's the foundation for longest palindrome and beyond, intuitive over Manacher's complexity. 𝕏

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#LeetCode #algorithm-tracing #algorithms #expand-around-centers #leetcode-647 #palindromic substrings #two pointers

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Originally reported by Dev.to

⚡ Key Takeaways

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