Longest Palindromic Substring

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Solution Guide: Longest Palindromic Substring

Approach

Expand around every odd and even center and keep the longest palindrome span encountered.

Complexity Analysis

Time
O(n^2)
Space
O(1)

Pattern

Expand Around Center

Why It Works

The longest palindrome must appear from some center expansion, so checking all centers guarantees optimality.

Updated Feb 2026