leviv / l33tc0de

My solutions to Leetcode problems!

6 Week LeetCode Homework!

For each week, try to solve as many problems as you can from each category!

Week 1

• Arrays:

  • https://leetcode.com/problems/sort-array-by-parity
  • https://leetcode.com/problems/transpose-matrix
  • https://leetcode.com/problems/flipping-an-image

• Basic math:

  • https://leetcode.com/problems/self-dividing-numbers
  • https://leetcode.com/problems/fizz-buzz
  • https://leetcode.com/problems/plus-one
  • https://leetcode.com/problems/excel-sheet-column-number
  • https://leetcode.com/problems/power-of-two

• Simple string manipulation:

  • https://leetcode.com/problems/reverse-string
  • https://leetcode.com/problems/detect-capital
  • https://leetcode.com/problems/reverse-words-in-a-string-iii
  • https://leetcode.com/problems/valid-palindrome
  • https://leetcode.com/problems/reverse-vowels-of-a-string
  • https://leetcode.com/problems/longest-common-prefix

• Simple bitwise manipulation:

  • https://leetcode.com/problems/number-complement
  • https://leetcode.com/problems/hamming-distance/
  • https://leetcode.com/problems/binary-gap
  • https://leetcode.com/problems/single-number

• Hashmaps and sets:

  • https://leetcode.com/problems/two-sum/
  • https://leetcode.com/problems/valid-anagram/

• Union find:

  • https://leetcode.com/problems/friend-circles
  • https://leetcode.com/problems/number-of-islands
  • https://leetcode.com/problems/surrounded-regions

Week 2

• Hash maps and hash sets
  • https://leetcode.com/problems/jewels-and-stones/
  • https://leetcode.com/problems/unique-morse-code-words/
  • https://leetcode.com/problems/happy-number/
  • https://leetcode.com/problems/uncommon-words-from-two-sentences/
  • https://leetcode.com/problems/distribute-candies/
  • https://leetcode.com/problems/groups-of-special-equivalent-strings/
  • https://leetcode.com/problems/intersection-of-two-arrays/
  • https://leetcode.com/problems/valid-sudoku/
  • https://leetcode.com/problems/isomorphic-strings/
  • https://leetcode.com/problems/word-pattern/
  • https://leetcode.com/problems/design-hashmap/
  • https://leetcode.com/problems/design-hashset/
• Multisets
  • https://leetcode.com/problems/find-all-anagrams-in-a-string/
    • Use a multiset for this one. You can also solve it without using one. How? Try to solve it both ways. How do the two solutions compare?
  • https://leetcode.com/problems/first-unique-character-in-a-string/
  • https://leetcode.com/problems/subdomain-visit-count/
  • https://leetcode.com/problems/find-the-difference/
  • https://leetcode.com/problems/most-common-word/
  • https://leetcode.com/problems/sort-characters-by-frequency/
  • https://leetcode.com/problems/set-mismatch/
    • This one has a few “clever” solutions but feel free to use a simple multiset solution.
  • https://leetcode.com/problems/number-of-atoms/
    • This one is more difficult than the average interview question but it is good exercise! You will need to build a simple parser in addition to using a multiset.
• Tries
  • https://leetcode.com/problems/longest-word-in-dictionary
  • https://leetcode.com/problems/implement-trie-prefix-tree
  • https://leetcode.com/problems/word-search-ii

Week 3

• Greedy algorithms

  • https://leetcode.com/problems/lemonade-change
  • https://leetcode.com/problems/assign-cookies
  • https://leetcode.com/problems/is-subsequence
  • https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons
  • https://leetcode.com/problems/partition-labels

• Binary search

  • https://leetcode.com/problems/binary-search
  • https://leetcode.com/problems/peak-index-in-a-mountain-array

• Sorting

  • https://leetcode.com/problems/valid-anagram
  • https://leetcode.com/problems/array-partition-i
  • https://leetcode.com/problems/merge-intervals
  • Use sorting, not a multiset (you solved this problem using a multiset last week) https://leetcode.com/problems/find-all-anagrams-in-a-string

• Recursion and memoization: make sure you use memoization if applicable for the problems below

  • https://leetcode.com/problems/powx-n
  • https://leetcode.com/problems/best-time-to-buy-and-sell-stock
  • https://leetcode.com/problems/edit-distance
  • https://leetcode.com/problems/house-robber-ii
  • Do not use a built-in regex for this one: https://leetcode.com/problems/regular-expression-matching/

• Dynamic Programming: same problems as above, but use dynamic programming this time

  • https://leetcode.com/problems/best-time-to-buy-and-sell-stock
  • https://leetcode.com/problems/edit-distance
  • https://leetcode.com/problems/house-robber-ii
  • Do not use a built-in regex for this one: https://leetcode.com/problems/regular-expression-matching/

Week 4

• Linked lists

  • https://leetcode.com/problems/reverse-linked-list

  • https://leetcode.com/problems/odd-even-linked-list

  • https://leetcode.com/problems/reverse-nodes-in-k-group

  • https://leetcode.com/problems/lru-cache

  • • Hint: This one is a bit harder. You will need to use a doubly linked list and a hash map to get O(1) time complexity for both operations.

• Stacks

  • https://leetcode.com/problems/baseball-game
  • https://leetcode.com/problems/next-greater-element-i
  • https://leetcode.com/problems/valid-parentheses
  • https://leetcode.com/problems/score-of-parentheses

• Queues

  • https://leetcode.com/problems/implement-stack-using-queues/
  • https://leetcode.com/problems/implement-queue-using-stacks/
  • https://leetcode.com/problems/rotate-array

• Heaps

  • https://leetcode.com/problems/top-k-frequent-elements
  • https://leetcode.com/problems/merge-k-sorted-lists

• Combinatorial generation

  • https://leetcode.com/problems/subsets
  • https://leetcode.com/problems/permutations
  • https://leetcode.com/problems/combinations
  • https://leetcode.com/problems/generate-parentheses
  • https://leetcode.com/problems/gray-code

• Backtracking

  • https://leetcode.com/problems/combination-sum
  • https://leetcode.com/problems/partition-equal-subset-sum
  • https://leetcode.com/problems/partition-to-k-equal-sum-subsets
  • https://leetcode.com/problems/sudoku-solver

Week 5

• Trees

  • https://leetcode.com/problems/n-ary-tree-postorder-traversal
  • https://leetcode.com/problems/leaf-similar-trees
  • https://leetcode.com/problems/same-tree
  • https://leetcode.com/problems/sum-of-left-leaves
  • https://leetcode.com/problems/diameter-of-binary-tree
  • https://leetcode.com/problems/longest-univalue-path
  • https://leetcode.com/problems/find-bottom-left-tree-value

• Graphs

  • https://leetcode.com/problems/course-schedule
  • https://leetcode.com/problems/island-perimeter
  • https://leetcode.com/problems/is-graph-bipartite
  • https://leetcode.com/problems/word-search
  • https://leetcode.com/problems/course-schedule-ii
  • https://leetcode.com/problems/longest-increasing-path-in-a-matrix
  • https://leetcode.com/problems/network-delay-time/

Week 6

Coding exercises

• Write a simple preforking echo server, without looking at the reference.
• Write a multithreaded merge-sort https://www.geeksforgeeks.org/merge-sort-using-multi-threading/

Reading and videos

Network

• https://jvns.ca/blog/2017/06/03/async-io-on-linux--select--poll--and-epoll/

• https://idea.popcount.org/2017-01-06-select-is-fundamentally-broken/

• https://www.youtube.com/watch?v=uwoD5YsGACg&vl=en

• https://www.howtogeek.com/190014/htg-explains-what-is-the-difference-between-tcp-and-udp/

• Python/Ruby

• • https://tomayko.com/blog/2009/unicorn-is-unix
  • https://gist.github.com/fuentesjr/240063
  • https://wiki.python.org/moin/UdpCommunication

Multithreading

• https://www.geeksforgeeks.org/mutex-vs-semaphore/

• https://stackoverflow.com/questions/34510/what-is-a-race-condition

• https://www.sitepoint.com/dangers-race-conditions/

• https://www.slashroot.in/difference-between-process-and-thread-linux

• Python

  • https://www.tutorialspoint.com/python/python_multithreading.htm
  • https://medium.com/@nbosco/multithreading-vs-multiprocessing-in-python-c7dc88b50b5b
  • https://docs.python.org/3/c-api/init.html#thread-state-and-the-global-interpreter-lock

• Java

  • https://winterbe.com/posts/2015/04/07/java8-concurrency-tutorial-thread-executor-examples/
  • https://winterbe.com/posts/2015/04/30/java8-concurrency-tutorial-synchronized-locks-examples/
  • https://winterbe.com/posts/2015/05/22/java8-concurrency-tutorial-atomic-concurrent-map-examples/

​ File system

• https://www.tecmint.com/explanation-of-everything-is-a-file-and-types-of-files-in-linux/
• http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/dev.html
• http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html