Problems
Callback's own problems and the LeetCode questions companies have been asking, in one place — filter by category, company, topic, difficulty, and how recently a question showed up.
Solve on Callback
7 problems asked at Meta — full prompts you can work right here.
Merge Overlapping Intervals
Algorithms & Data Structures · Sort, then sweep — the pattern behind a dozen calendar problems.
Design an LRU Cache
Algorithms & Data Structures · Hash map plus doubly linked list, all operations O(1).
Implement debounce()
Frontend · Closures and timers, the frontend screen classic.
Design a News Feed
System Design · Fan-out on write vs. read, ranking, and the celebrity problem.
Build a Counter
Frontend · The React warm-up: state, events, and a derived disable.
Build a Todo List
Frontend · List state done right: keys, controlled input, and deletes.
Build Tabs
Frontend · One active index drives the whole component.
Asked on LeetCode
1,399 questions at Meta · all time
- Minimum Remove to Make Valid ParenthesesmediumStringStackfrequency 100.0
- Valid Word AbbreviationeasyTwo PointersStringfrequency 96.8
- Valid Palindrome IIeasyTwo PointersStringGreedyfrequency 95.1
- Binary Tree Vertical Order TraversalmediumHash TableTreeDepth-First SearchBreadth-First Search+2frequency 93.4
- Kth Largest Element in an ArraymediumArrayDivide and ConquerSortingHeap (Priority Queue)+1frequency 93.3
- Two SumeasyArrayHash Tablefrequency 90.2
- Basic Calculator IImediumMathStringStackfrequency 89.3
- Lowest Common Ancestor of a Binary Tree IIImediumHash TableTwo PointersTreeBinary Tree+2frequency 88.5
- Nested List Weight SummediumDepth-First SearchBreadth-First Searchfrequency 87.9
- Random Pick with WeightmediumArrayMathBinary SearchPrefix Sum+1frequency 87.7
- Subarray Sum Equals KmediumArrayHash TablePrefix Sumfrequency 87.2
- Diameter of Binary TreeeasyTreeDepth-First SearchBinary TreeDP on Treesfrequency 86.8
- Lowest Common Ancestor of a Binary TreemediumTreeDepth-First SearchBinary TreeBinary Lifting+1frequency 86.4
- Merge Sorted ArrayeasyArrayTwo PointersSortingfrequency 86.3
- Find Peak ElementmediumArrayBinary Searchfrequency 85.8
- Binary Tree Right Side ViewmediumTreeDepth-First SearchBreadth-First SearchBinary Treefrequency 85.4
- Merge IntervalsmediumArraySortingQuicksortfrequency 84.6
- Pow(x, n)mediumMathRecursionfrequency 84.1
- Simplify PathmediumStringStackfrequency 83.7
- Buildings With an Ocean ViewmediumArrayStackMonotonic Stackfrequency 82.6
- Valid PalindromeeasyTwo PointersStringfrequency 82.6
- Best Time to Buy and Sell StockeasyArrayDynamic Programmingfrequency 82.2
- Top K Frequent ElementsmediumArrayHash TableDivide and ConquerSorting+4frequency 81.3
- Shortest Path in Binary MatrixmediumArrayBreadth-First SearchMatrixfrequency 80.9
- Dot Product of Two Sparse VectorsmediumArrayHash TableTwo PointersDesign+1frequency 79.6
- Next PermutationmediumArrayTwo Pointersfrequency 79.0
- LRU CachemediumHash TableLinked ListDesignDoubly-Linked Listfrequency 78.5
- Sum Root to Leaf NumbersmediumTreeDepth-First SearchBinary Treefrequency 78.4
- Copy List with Random PointermediumHash TableLinked Listfrequency 78.1
- Range Sum of BSTeasyTreeDepth-First SearchBinary Search TreeBinary Treefrequency 78.0
- K Closest Points to OriginmediumArrayMathDivide and ConquerGeometry+4frequency 77.1
- Merge k Sorted ListshardLinked ListDivide and ConquerHeap (Priority Queue)Merge Sort+1frequency 75.1
- Max Consecutive Ones IIImediumArrayBinary SearchSliding WindowPrefix Sumfrequency 74.6
- Valid ParentheseseasyStringStackBracket Sequencesfrequency 73.9
- Add Two NumbersmediumLinked ListMathRecursionfrequency 73.6
- Interval List IntersectionsmediumArrayTwo PointersSweep Linefrequency 73.6
- Find First and Last Position of Element in Sorted ArraymediumArrayBinary Searchfrequency 73.1
- Moving Average from Data StreameasyArrayDesignQueueData Streamfrequency 73.1
- Custom Sort StringmediumHash TableStringSortingfrequency 72.8
- Making A Large IslandhardArrayDepth-First SearchBreadth-First SearchUnion-Find+1frequency 72.8
- Minimum Window SubstringhardHash TableStringSliding Windowfrequency 71.9
- Minimum Add to Make Parentheses ValidmediumStringStackGreedyBracket Sequencesfrequency 71.8
- Maximum SwapmediumMathGreedyfrequency 71.7
- 3SummediumArrayTwo PointersSortingfrequency 71.1
- Clone GraphmediumHash TableDepth-First SearchBreadth-First SearchGraph Theoryfrequency 70.5
- Longest Common PrefixeasyArrayStringTriefrequency 69.7
- Vertical Order Traversal of a Binary TreehardHash TableTreeDepth-First SearchBreadth-First Search+2frequency 69.1
- Longest Substring Without Repeating CharactersmediumHash TableStringSliding Windowfrequency 68.9
- Kth Missing Positive NumbereasyArrayBinary Searchfrequency 68.6
- Valid NumberhardStringfrequency 68.2
Listings only — titles, difficulty, and tags link out to LeetCode. Imported from the leetcode-company-wise-problems snapshot dated 1 June 2025. Frequency is that dataset's own relative score within a company and time range.