This my personal list of recommended problems to do for interview preparation. Aim to be able to do mediums in < 30 mins. NOTE:

• A problem often has valid approaches other than the category it's under.
• The fact there is a category at all is often a large hint that you would not normally have.

Graphs

• https://leetcode.com/problems/number-of-islands/
• https://leetcode.com/problems/course-schedule/
• https://leetcode.com/problems/course-schedule-ii/
• https://leetcode.com/problems/rotting-oranges/
• https://leetcode.com/problems/pacific-atlantic-water-flow/
• https://leetcode.com/problems/word-search/

Arrays

• https://leetcode.com/problems/product-of-array-except-self/
• https://leetcode.com/problems/maximum-subarray/
• https://leetcode.com/problems/best-time-to-buy-and-sell-stock/
• https://leetcode.com/problems/move-zeroes/
• https://leetcode.com/problems/3sum/

Hashes

• https://leetcode.com/problems/two-sum/
• https://leetcode.com/problems/group-anagrams/

Linked Lists

• https://leetcode.com/problems/reverse-linked-list/
• https://leetcode.com/problems/linked-list-cycle/
• https://leetcode.com/problems/merge-two-sorted-lists/

2D Arrays

• https://leetcode.com/problems/spiral-matrix/
• https://leetcode.com/problems/search-a-2d-matrix/
• https://leetcode.com/problems/set-matrix-zeroes/

Sorting

• https://leetcode.com/problems/merge-intervals/

Strings

• https://leetcode.com/problems/positions-of-large-groups/
• https://leetcode.com/problems/valid-anagram/
• https://leetcode.com/problems/longest-palindromic-substring/
• https://leetcode.com/problems/longest-substring-without-repeating-characters/
• https://leetcode.com/problems/add-strings

Trees

• https://leetcode.com/problems/maximum-depth-of-binary-tree/
• https://leetcode.com/problems/kth-smallest-element-in-a-bst/
• https://leetcode.com/problems/time-needed-to-inform-all-employees/

Heaps

• https://leetcode.com/problems/top-k-frequent-elements/
• https://leetcode.com/problems/kth-largest-element-in-an-array/

Tries

• https://leetcode.com/problems/implement-trie-prefix-tree/
• https://leetcode.com/problems/word-search-ii/

Queues / Stacks

• https://leetcode.com/problems/implement-queue-using-stacks/
• https://leetcode.com/problems/valid-parentheses/

Monotonic Stacks and Sequences

• https://leetcode.com/problems/check-if-array-is-sorted-and-rotated/
• https://leetcode.com/problems/daily-temperatures
• https://leetcode.com/problems/largest-rectangle-in-histogram/

Recursion

• https://leetcode.com/problems/subsets/

Two Pointer / Sliding Window

• https://leetcode.com/problems/valid-palindrome/
• https://leetcode.com/problems/container-with-most-water/

Dynamic Programming

• https://leetcode.com/problems/unique-paths/
• https://leetcode.com/problems/coin-change/
• https://leetcode.com/problems/best-time-to-buy-and-sell-stock/
• https://leetcode.com/problems/longest-increasing-subsequence

Math / Binary

• https://leetcode.com/problems/missing-number/

Combining Data Structures

• https://leetcode.com/problems/lru-cache/
• https://leetcode.com/problems/insert-delete-getrandom-o1/

Binary Search

• https://leetcode.com/problems/search-in-rotated-sorted-array/
• https://leetcode.com/problems/capacity-to-ship-packages-within-d-days
• https://leetcode.com/problems/koko-eating-bananas/

Greedy

• https://leetcode.com/problems/task-scheduler/

Disjoint Sets and Union Find

• https://leetcode.com/problems/min-cost-to-connect-all-points/
• https://leetcode.com/problems/number-of-operations-to-make-network-connected/

:) ?

• https://leetcode.com/problems/trapping-rain-water/
• https://leetcode.com/problems/median-of-two-sorted-arrays/