A.13: Open Practice

Introduction
The following is a list of curated Leetcode problems we can work on daily after learning algorithms fundamentals. The problems are taken from the Top Interview Questions list in Leetcode, sorted in decreasing acceptance rate, i.e. % of submissions that were accepted on Leetcode.
The majority of algorithms interviews Rocket grads have encountered have focused on arrays and hash tables. If you find yourself stuck on a problem focusing on a different data structure, feel free to skip and focus on the array and hash tables problems first.
Exercises
Day 1
1.​https://leetcode.com/problems/reverse-string/​
2.​https://leetcode.com/problems/maximum-depth-of-binary-tree/​
3.​https://leetcode.com/problems/single-number/​
Day 2
1.​https://leetcode.com/problems/binary-tree-inorder-traversal/​
1.Feel free to skip the follow up question to implement this traversal iteratively. The iterative implementation is challenging and unlikely to appear in coding interviews.
2.​https://leetcode.com/problems/reverse-linked-list/​
1.FTBC3 strategy video: https://youtu.be/a5fTAdAv3_A?t=3101​
3.​https://leetcode.com/problems/subsets/​
Day 3
1.​https://leetcode.com/problems/fizz-buzz/​
2.​https://leetcode.com/problems/kth-smallest-element-in-a-bst/​
1.Hint: How can we traverse a BST in sorted order?
3.​https://leetcode.com/problems/top-k-frequent-elements/​
1.Hint: Recall our solution to the kth-largest element in a stream problem: https://leetcode.com/problems/kth-largest-element-in-a-stream/​
Day 4
1.​https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/​
1.Hint: To instantiate a TreeNode class, the syntax is new_node = TreeNode(...), replacing ... with the initialisation parameters.
2.​https://leetcode.com/problems/product-of-array-except-self/​
1.Hint: Solving this in O(n) without division is a bit of a trick. Feel free to solve it with division and move on.
2.If you're keen on solving it without division: Can we pre-process the data and create intermediate data structures in O(n) time such that we can then fill in the answer array with a single loop?
Day 5
1.​https://leetcode.com/problems/valid-anagram/​
2.​https://leetcode.com/problems/group-anagrams/​
1.Hint: What combination of arrays and hash tables can we use to group anagrams?
2.Rocket solution code: https://pastebin.com/pfM6JiTx​
3.Rocket solution video: https://youtu.be/yVCKfkJWHfQ?t=5281​
Day 6
1.​https://leetcode.com/problems/kth-largest-element-in-an-array/​
2.​https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/​
Day 7
1.​https://leetcode.com/problems/move-zeroes/​
2.​https://leetcode.com/problems/odd-even-linked-list/​
3.[REMOVE] https://leetcode.com/problems/excel-sheet-column-number/​
1.Hint: This is a base-26 numbering system. Requires a more math background to understand how numbers and exponents work. Feel free to skip.
Day 8
1.​https://leetcode.com/problems/roman-to-integer/​
2.​https://leetcode.com/problems/binary-tree-level-order-traversal/​
1.Rocket solution code: https://pastebin.com/P6qJZfux​
2.FTBC3 solution video: https://youtu.be/J0gohhbwN0w?t=6464​
3.​https://leetcode.com/problems/contains-duplicate/​
Day 9
1.​https://leetcode.com/problems/merge-two-sorted-lists/​
1.Rocket solution code: https://pastebin.com/GFxESn8Q​
2.FTBC3 solution video: https://youtu.be/3mFkTJ1vvyA?t=2492​
2.​https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/​
Day 10
1.​https://leetcode.com/problems/pascals-triangle/​
2.​https://leetcode.com/problems/unique-paths/​
Day 11
1.​https://leetcode.com/problems/flatten-nested-list-iterator/​
1.Completing this problem will help us understand how to use and implement classes in Python.
2.Hint: An iterator works like this: Each time we call next() on the iterator it will return the next element in the collection. When the iterator is "exhausted", i.e. we have reached the end of the collection, next() will return None.
3.Hint: For a refresher on how to use and implement classes in Python, see code examples from RA's OOP module.
2.​https://leetcode.com/problems/4sum-ii/​
Day 12
1.​https://leetcode.com/problems/number-of-1-bits/​
2.​https://leetcode.com/problems/first-unique-character-in-a-string/​
Day 13
1.​https://leetcode.com/problems/container-with-most-water/​
2.​https://leetcode.com/problems/palindrome-partitioning/​
Day 14
1.​https://leetcode.com/problems/implement-trie-prefix-tree/​
2.​https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/​
Day 15
1.​https://leetcode.com/problems/intersection-of-two-arrays-ii/​
2.​https://leetcode.com/problems/best-time-to-buy-and-sell-stock/​
Day 16
1.​https://leetcode.com/problems/trapping-rain-water/​
Day 17
1.​https://leetcode.com/problems/happy-number/​
2.​https://leetcode.com/problems/valid-sudoku/​
Day 18
1.​https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/​
2.​https://leetcode.com/problems/populating-next-right-pointers-in-each-node/​
Day 19
1.​https://leetcode.com/problems/serialize-and-deserialize-binary-tree/​
Day 20
1.​https://leetcode.com/problems/letter-combinations-of-a-phone-number/​
1.FTBC3 solution video: https://youtu.be/Ha4iqs1ze2E?t=2831​
2.​https://leetcode.com/problems/number-of-islands/​
Day 21
1.​https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/​
2.​https://leetcode.com/problems/perfect-squares/​
Day 22
1.​https://leetcode.com/problems/insert-delete-getrandom-o1/​
Day 23
1.​https://leetcode.com/problems/climbing-stairs/​
2.​https://leetcode.com/problems/symmetric-tree/​
3.​https://leetcode.com/problems/maximum-subarray/​
Day 24
1.​https://leetcode.com/problems/find-median-from-data-stream/​
Day 25
1.​https://leetcode.com/problems/min-stack/​
2.​https://leetcode.com/problems/two-sum/​
Day 26
1.​https://leetcode.com/problems/sort-list/​
2.​https://leetcode.com/problems/longest-consecutive-sequence/​
Day 27
1.​https://leetcode.com/problems/search-a-2d-matrix-ii/​
2.​https://leetcode.com/problems/sliding-window-maximum/​
Day 28
1.​https://leetcode.com/problems/longest-increasing-path-in-a-matrix/​
Day 29
1.​https://leetcode.com/problems/set-matrix-zeroes/​
2.​https://leetcode.com/problems/course-schedule/​
Day 30
1.​https://leetcode.com/problems/intersection-of-two-linked-lists/​
2.​https://leetcode.com/problems/longest-increasing-subsequence/​
Day 31
1.​https://leetcode.com/problems/linked-list-cycle/​
2.​https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/​
Day 32
1.​https://leetcode.com/problems/house-robber/​
2.​https://leetcode.com/problems/course-schedule-ii/​
Day 33
1.​https://leetcode.com/problems/merge-k-sorted-lists/​
2.​https://leetcode.com/problems/reverse-bits/​
Day 34
1.​https://leetcode.com/problems/count-of-smaller-numbers-after-self/​
Day 35
1.​https://leetcode.com/problems/word-break/​
2.​https://leetcode.com/problems/gas-station/​
Day 36
1.​https://leetcode.com/problems/palindrome-linked-list/​
2.​https://leetcode.com/problems/merge-intervals/​
Day 37
1.​https://leetcode.com/problems/copy-list-with-random-pointer/​
Day 38
1.​https://leetcode.com/problems/valid-parentheses/​
2.​https://leetcode.com/problems/merge-sorted-array/​
1.FTBC3 solution video: https://youtu.be/qRgOAQlNhVE?t=4814​
3.​https://leetcode.com/problems/increasing-triplet-subsequence/​
Day 39
1.​https://leetcode.com/problems/basic-calculator-ii/​
2.​https://leetcode.com/problems/evaluate-reverse-polish-notation/​
Day 40
1.​https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/​
2.​https://leetcode.com/problems/coin-change/​

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A.12: Bit Manipulation

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IP.0: Interview Prep Overview

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