Expanding From Center (Palindromes) — Two Pointers
The Expanding From Center (Palindromes) pattern applies when you need the Expanding From Center (Palindromes) technique within the Two Pointers pattern. Its time complexity is O(n²) and space complexity O(1). It is used in 2 problems on Thita, including Longest Palindromic Substring and Palindromic Substrings. Common variations are String Comparison with Backspaces and String Reversal.
Master the expand from center technique for finding palindromic substrings and longest palindrome problems.
Expanding From Center (Palindromes) is one of the 7 subpatterns of the Two Pointers pattern, which covers fast-slow, converging, expanding from center, and in-place modification techniques. The whole pattern is about 3 hours of study. This subpattern is a core technique: expect it to come up directly in interviews.
What Expanding From Center (Palindromes) covers
Master the two pointers technique including fast-slow pointers, converging pointers, and expanding from center. Essential for array, string, and linked list problems in coding interviews. Problems in this subpattern are usually searched for as expand from center, longest palindrome, palindromic substring, palindrome detection, leetcode 5, leetcode 647.
How to practise Expanding From Center (Palindromes) on Thita.ai
Read the theory for Expanding From Center (Palindromes), then work the problems attached to it in the browser editor. Your solution runs against the problem's test cases, and the AI coach offers a hint about the technique you are missing rather than a finished solution. Progress is tracked per subpattern, so the Two Pointers tracker shows this one as covered once you have solved its problems.
Other subpatterns in Two Pointers
- Fast & Slow (Cycle Detection) — Master Floyd's tortoise and hare algorithm for cycle detection. Detect cycles in linked lists and find duplicate numbers.
- Converging (Sorted Array Target Sum) — Learn converging two pointers for sorted arrays. Solve two sum, three sum, and container problems efficiently.
- In-place Array Modification — Learn in-place array modification using two pointers. Remove duplicates, move zeroes, and sort colors efficiently.
- String Comparison with Backspaces — Learn to compare strings with backspace characters using two pointers from the end.
- String Reversal — Master string reversal techniques including reverse string, reverse words, and reverse vowels using two pointers.
- Fixed Separation (Nth Node from End) — Master fixed separation two pointers to find nth node from end, middle of list, and similar problems.
Related DSA patterns
- Sliding Window — Fixed-size, variable-size, and character frequency matching window techniques.
- Binary Search Patterns — Standard binary search, rotated arrays, first/last occurrence, and search on answer space.
- Array/Matrix Manipulation Patterns — In-place operations, hashing, prefix sums, spiral traversal, and cyclic sort.
- Linked List Manipulation Patterns — In-place reversal, merging sorted lists, reordering, and intersection detection.
Where to go next
Expanding From Center (Palindromes) is one lesson in a 16-pattern DSA course. If you are preparing end to end, work the interview-critical patterns first and use the pattern sheet as the checklist; if you are here for one technique, the Two Pointers guide is the shortest path back to the rest of it.