GitHub - hereisderek/code_practice: coding practice, mostly on leetcode

Code practice link

Templates

Difficulty	Marks	link
🟢	✅❗❓❌	Leetcode
🟠	✅❗❓❌	Leetcode
🔴	✅❗❓❌	Leetcode

Markers:

✅/✔️ For finished
👷 For working in progress
❌ For unfinished due to complicity or challenging
❗For marking good questions
❓with doubt or unfinished
~~Strikedthrough~~ For not bothering (e.g. too easy)
MARK in code for paying extra attention

Difficulties:

🟢(Easy)
🟠(Medium)
🔴(Hard) 🤨

Kotlin

Since I use kotlin, I have created some convenient utility functions, mostly for testing/debugging purpose. (I might just create a branch with just the utility functions, however.. )

Note: To enable assertion for kotlin, pass in -ea as jvm launch argument, see this link

Other than those listed below, check out _util.kt for more

Run timed tests on a list of method variable. Sample usage checkout this Update: I noticed that this method may not be accurate, not sure of the cause

@OptIn(ExperimentalTime::class)
inline fun<reified T : KCallable<*>, reified R> List<T>.runTimedTests(
    testName: String? = Thread.currentThread().stackTrace.getOrNull(1)?.className?.split("$", limit = 0)?.get(0),
    printTime: Boolean = true,
    block: T.()->R
) {
    forEachIndexed { index, it ->
        val timeValue = measureTimedValue{ it.block() }
        val prefix = if (testName.isNullOrEmpty()) "" else "${testName}."
        if (printTime) println("execution for ${prefix}${it.name} finished, took ${timeValue.duration.inWholeNanoseconds} Nanoseconds")
    }
}

Sample print out:

execution for _2022._05.Leetcode_15.MY1.threeSum finished, took 476348 Nanoseconds
execution for _2022._05.Leetcode_15.MY1.threeSum finished, took 423606 Nanoseconds
execution for _2022._05.Leetcode_15.MY2.threeSum finished, took 435733 Nanoseconds

Assertion (assertEqual)

test() assertEqual "expected" // for single answer
test().assertEqual("possible_output1", "possible_output2") // for multiple correct answers

Build-in data types
1. Node (typealias IntNode = Node<Int>) and some built-in functions, e.g:
  1. fun <T> linkedNodesOf(vararg nodes: T) : Node<T> usage:linkedNodesOf(1, 2, 3) to create a linked nodes like 1 -> 2 -> 3
  2. fun <T> Node<T>.toList() : List<T> usage: linkedNodesOf(1, 2, 3).toList() gets: [1,2,3]
  3. fun <T, R> Node<T>.mapValue(transform: ((T)->R)) : List<R> usage: linkedNodesOf(1, 2, 3).mapValue{ it * 2 } gets [2,4,6]
  4. others see this file: Node

202205

20220528

youngyangyang04/leetcode-master/0001.两数之和.md · GitHub

Marks	link	Notes
🟢✅	1. Two Sum
🟢✅	342. Valid Anagram
🟢✅	349. Intersection of Two Arrays
🟢	~~383. Ransom Note~~
🟢✅	49. Group Anagrams

20220529, 20220601

youngyangyang04/leetcode-master/0005.最长回文子串.md · GitHub

Marks	link	Notes
🟠✅	647. Palindromic Substrings
🟠❗❓	5. Longest Palindromic Substring

20220602, 20220605, 20220606

youngyangyang04/leetcode-master/0005.最长回文子串.md · GitHub

Difficulty	Marks	link	Notes
Medium	✅❗	5. Longest Palindromic Substring [leetcode] [git]
Medium	✅	15. 3Sum 💃💃💃 [leetcode] [git]	My4 not done

20220606

Difficulty	Marks	Name	link	Notes
Easy	🟠✅
Medium	🟢✅	17. Letter Combinations of a Phone Number	Leetcode Github	Didn't read the sample code since it didn't take me too much thinking to solve the question, but it might worth a read
Medium	Skipped for now	18. 4Sum 💃💃💃💃	Leetcode Github
Medium	🟠❓	19. Remove Nth Node From End of List	Leetcode Github

20220607 labuladong

Difficulty	Marks	Name	link	Notes
Easy	🟢✅	21. Merge Two Sorted Lists	Leetcode labuladong	Sample1 is interesting (recursion)
Easy	🟢✅	141. Linked List Cycle	Leetcode
Medium	❗	142. Linked List Cycle II	Leetcode labuladong

20220608,20220614 labuladong

Difficulty	Marks	Name	link	Notes
Hard	🟢✅	23. Merge k Sorted Lists	Leetcode labuladong	Need to read the sample code
Easy	❗	160. Intersection of Two Linked Lists	Leetcode labuladong	Sample1 is interesting (recursion)

20220614,20220615

labuladong

Difficulty	Marks	Name	link	Notes
Easy	🟢	876. Middle of the Linked List	Leetcode	Faster than 100% submission 🟢🟢
Medium	❗	92. Reverse Linked List II	Leetcode	My2
Easy	🟠✅	206. Reverse Linked List	Leetcode	Need to check sample and read this and read S1

20220615,20220615

Difficulty	Marks	Name	link	Notes
Hard	🔴❗❗❓	25. Reverse Nodes in k-Group	Leetcode

TODO:

https://labuladong.github.io/algo/2/17/18/

20220616

Difficulty	Marks	Name	link
🟢	❌	234. Palindrome Linked List	Leetcode
🟢	✅	26. Remove Duplicates from Sorted Array	Leetcode
🟢	✅	27. Remove Element	Leetcode
🟢	✅	83. Remove Duplicates from Sorted List	Leetcode

TODO: Leetcode_710

20220617

Difficulty	Marks	Name	link	Notes
🟠	✅🟢	167. Two Sum II - Input Array Is Sorted	Leetcode
🟢	✅	283. Move Zeroes	Leetcode

20220618

Difficulty	Marks	Name	link
🟢	✅	344. Reverse String	Leetcode
🟢	✅	303. Range Sum Query - Immutable	Leetcode
🟠	✅	304. Range Sum Query 2D - Immutable	Leetcode

Leetcode 370: Range Addition

20220619

Difficulty	Marks	Name	link	Notes
🟠	❓	~~370: Range Addition~~	Leetcode	Put off for now
🟠	✅🟢	1094. Car Pooling	Leetcode
🟠	❓	~~1109. Corporate Flight Bookings~~	Leetcode
🟠	❓	48. Rotate Image	Leetcode

20220620

Difficulty	Marks	Name	link	Notes
🟠	✅	54. Spiral Matrix	Leetcode

20220621

Difficulty	Marks	Name	link	Notes
🟠	❓	59. Spiral Matrix II	Leetcode
🟠	✅❓	3. Longest Substring Without Repeating Characters	Leetcode	TODO: read explanation

20220627,20200630

Difficulty	Name	link
🔴	76. Minimum Window Substring	Leetcode
🟠	34. Find First and Last Position of Element in Sorted Array	Leetcode
🟠	1109. Corporate Flight Bookings	Leetcode

20220701

Difficulty	Marks	Name	link	Notes
🟠	✅	11. Container With Most Water	Leetcode
🔴	✅❗❓❌	42. Trapping Rain Water	Leetcode

20220702

Difficulty	Marks	Name	link	Notes
🟠	✅	238. Product of Array Except Self	Leetcode
🟢	✅	217. Contains Duplicate	Leetcode
🟠	✅	347. Top K Frequent Elements	Leetcode	1. Heatmap, 2. bucket list/sort
🟢	✅	125. Valid Palindrome	Leetcode
🟠	✅	271. Encode and Decode Strings	Lintcode_659

20220703

Difficulty	Marks	Name	link
🟠	✅	128. Longest Consecutive Sequence	Leetcode
🟢	✅	121. Best Time to Buy and Sell Stock	Leetcode
🟠	✅❓	424. Longest Repeating Character Replacement	Leetcode
🟠	✅	567. Permutation in String	Leetcode

20220704

Difficulty	Marks	Name	link	Notes
🔴	✅❗❓❌	239. Sliding Window Maximum	Leetcode
🟢	✅	20. Valid Parentheses	Leetcode
🟠	✅❗	155. Min Stack	Leetcode	The use of miniStack in S1 and S2

20220705

Difficulty	Marks	Name	link
🟠	✅	150. Evaluate Reverse Polish Notation	Leetcode
🟠	✅❓	22. Generate Parentheses	Leetcode
🟢	✅❗❓❌	496. Next Greater Element I	Leetcode

20220724

Difficulty	Marks	Name	link	Notes
🟠	✅	739. Daily Temperatures	Leetcode
🟠	✅	853. Car Fleet	Leetcode

                                        |            |

20220725

Difficulty	Marks	Name	link
🔴	❌	84. Largest Rectangle in Histogram	Leetcode
🟢	✅	704. Binary Search	Leetcode
🟠	✅	74. Search a 2D Matrix	Leetcode
🟠	✅❗	875. Koko Eating Bananas	Leetcode
🟠	❌	33. Search in Rotated Sorted Array	Leetcode

🟢	✅❗❓❌		Leetcode
🟠	✅❗❓❌		Leetcode
🔴	✅❗❓❌		Leetcode

20220726

Difficulty	Marks	Name	link
🟠	✅❗❓❌	143. Reorder List	Leetcode
🟢	✅❗❓❌		Leetcode
🟠	✅❗❓❌		Leetcode
🔴	✅❗❓❌		Leetcode

20220727

Difficulty	Marks	Name	link	Notes
🟠	✅	138. Copy List with Random Pointer	Leetcode

2022078

Difficulty	Marks	Name	link
🟠	✅	2. Add Two Numbers	Leetcode
🟠	❌	287. Find the Duplicate Number	Leetcode
🟠	❌	146. LRU Cache	Leetcode

20220729

Difficulty	Marks	Name	link
🟢	✅	226. Invert Binary Tree	Leetcode
🟢	✅❗	104. Maximum Depth of Binary Tree	Leetcode
🟢	✅	110. Balanced Binary Tree	Leetcode
🟢	✅	100. Same Tree	Leetcode
🟢	✅❗	572. Subtree of Another Tree	Leetcode

572: can use a utility method isSameTree to check or need to be careful (see solution)

20220730

Difficulty	Marks	Name	link
🟢	✅	235. Lowest Common Ancestor of a Binary Search Tree	Leetcode
🟢	✅❗❓❌	703. Kth Largest Element in a Stream	Leetcode
🟢	✅	1046. Last Stone Weight	Leetcode
🟢	✅	70. Climbing Stairs	Leetcode
🟢	✅	746. Min Cost Climbing Stairs	Leetcode
🟢	✅❗❓❌		Leetcode
🟠	✅❗❓❌		Leetcode
🔴	✅❗❓❌		Leetcode

235: Binary search tree: left <= val <= right
746: Build an array dp where dp[i] is the minimum cost to climb to the top starting from the ith staircase.

20220731

Difficulty	Marks	Name	link
🟢	✅	136. Single Number	Leetcode
🟢	✅❗	191. Number of 1 Bits	Leetcode
🟢	❌	338. Counting Bits	Leetcode
🟢	✅	190. Reverse Bits	Leetcode
🟢	✅❗❓❌	268. Missing Number	Leetcode

191: use mod n = n % 2

20220802

Difficulty	Marks	Name	link	Notes
🟠	✅	208. Implement Trie (Prefix Tree)	Leetcode
🟠	❓	211. Design Add and Search Words Data Structure	Leetcode
🟠	✅	981. Time Based Key-Value Store	Leetcode
🟠	✅	973. K Closest Points to Origin	Leetcode
🟠	✅	215. Kth Largest Element in an Array	Leetcode
🟠	✅	78. Subsets	Leetcode	try to solve with single res: ArrayList
🟠	✅❗❓❌	39. Combination Sum	Leetcode	S1

20220803

Difficulty	Marks	Name	link	Notes
🟠	✅	46. Permutations	Leetcode
🟠	✅❗❓❌	90. Subsets II	Leetcode

20220804

Difficulty	Marks	Name	link	Notes
🟠	❓	40. Combination Sum II	Leetcode
🟠	✅❗	200. Number of Islands	Leetcode

20220805

Difficulty	Marks	Name	link	Notes
🟠	✅❗❓❌	695. Max Area of Island	Leetcode
🟠	✅❗❓❌	133. Clone Graph	Leetcode

20220806

Difficulty	Marks	Name	link	Notes
🟠	✅	417. Pacific Atlantic Water Flow	Leetcode	revert: ocean to land
🟠	✅❗❓❌	130. Surrounded Regions	Leetcode

Note:

130: reverse thinking, thanks all non-surrounded region to T and change all O to X then change Ts back to O

20220807

Difficulty	Marks	Name	link	Notes
🟠	✅❗	198. House Robber	Leetcode

20220808

Difficulty	Marks	Name	link	Notes
🟠	✅❗❓❌	322. Coin Change	Leetcode
🟠	✅❗❓❌	91. Decode Ways	Leetcode

20220810

Difficulty	Marks	Name	link	Notes
🟠	✅	36. Valid Sudoku	Leetcode
🟠	✅❗❓❌	53. Maximum Subarray	Leetcode

20220811

Difficulty	Marks	Name	link
🟠	✅❗	134. Gas Station	Leetcode
🟠	✅❓❓	55. Jump Game	Leetcode
🟠	✅❓	45. Jump Game II	Leetcode

Notes:

55: M4
134: S1

20220812

Difficulty	Marks	Name	link	Notes
🟠	✅	846. Hand of Straights	Leetcode
🟠	✅❓	57. Insert Interval	Leetcode

20220813

Difficulty	Marks	Name	link	Notes
🟠	✅❗❓❌	102. Binary Tree Level Order Traversal	Leetcode

20220814

Difficulty	Marks	Name	link
🟠	✅	199. Binary Tree Right Side View	Leetcode
🟠	✅	1448. Count Good Nodes in Binary Tree	Leetcode
🟠	✅	98. Validate Binary Search Tree	Leetcode
🟠	✅❗	230. Kth Smallest Element in a BST	Leetcode
🟠	✅❗❗❗	105. Construct Binary Tree from Preorder and Inorder Traversal	Leetcode
🟠	✅❗❓❌	211. Design Add and Search Words Data Structure	Leetcode
🟠	✅❓	621. Task Scheduler	Leetcode

Notes:

bfs - order level traversal
98: binary search tree - sorted order
230: solution

20220815

Difficulty	Marks	Name	link
🟢	✅❗❓❌		Leetcode
🟠	✅❓	355. Design Twitter	Leetcode
🟠	✅	332. Reconstruct Itinerary	Leetcode
🟠	✅❓	1584. Min Cost to Connect All Points	Leetcode

Notes:

1584: Read S2 and link

2022081

Difficulty	Marks	Name	link
🟢	✅❗❓❌		Leetcode
🟠	✅	143. Reorder List	Leetcode
🟠	✅	146. LRU Cache	Leetcode
🟠	✅	23. Merge k Sorted Lists	Leetcode
🔴	✅	25. Reverse Nodes in k-Group	Leetcode
🟠		211. Design Add and Search Words Data Structure	Leetcode
🟠	❗❓❌	4. Median of Two Sorted Arrays	Leetcode
🟠	✅	130. Surrounded Regions	Leetcode

Notes:!!

143: slow -> 0 and fast -> 1, fast jumps two steps while slow jumps one, when fast became null slow is at the end of the first half

202208

Difficulty	Marks	Name	link
🟠	✅❗❓❌	743. Network Delay Time	Leetcode
🟠	✅❗❓❌	295. Find Median from Data Stream	Leetcode

20220824

Difficulty	Marks	Name	link
🟠	✅	79. Word Search	Leetcode

20220825

Difficulty	Marks	Name	link
🟠	❌	131. Palindrome Partitioning	Leetcode
🟠	✅❗❓❌	17. Letter Combinations of a Phone Number	Leetcode

20220826

Difficulty	Marks	Name	link
🟠	✅	663 · Walls and Gates	Leetcode
🟠	✅	207. Course Schedule	Leetcode

207: S1

20220827

Difficulty	Marks	Name	link
🟠	✅❗❓❌	684. Redundant Connection	[Leetcode](// https://leetcode.com/problems/redundant-connection/)

20220828

Difficulty	Marks	Name	link
🟠	✅	2385. Amount of Time for Binary Tree to Be Infected	Leetcode

2385: S1

20220829

Difficulty	Marks	Name	link
🔴	✅❗❓❌	4. Median of Two Sorted Arrays	Leetcode

20220907

Difficulty	Marks	Name	link
🟠	✅❗❓❌	8. String to Integer (atoi)	Leetcode
🟠	✅❗❓❌	56. Merge Intervals	Leetcode

8: stupid ass question, not worth looking at

20220908

Difficulty	Marks	Name	link
🟠	❌	435. Non-overlapping Intervals	Leetcode
🟠	✅❗❓❌	Lintcode 919 · Meeting Rooms II	Leetcode youtube

20220911

Difficulty	Marks	Name	link
🟠	✅		Leetcode
🟠	✅	73. Set Matrix Zeroes	Leetcode
🟠	✅	50. Pow(x, n)	Leetcode
🟠	❌	371. Sum of Two Integers	Leetcode
🟢	✅	202. Happy Number	Leetcode
🟢	✅	66. Plus One	Leetcode

20220912

Difficulty	Marks	Name	link
🟠	✅	338. Counting Bits	Leetcode
🟠	✅❗❓❌	91. Decode Ways	Leetcode

20220914

Difficulty	Marks	Name	link
🟠	✅❗❓❌	213. House Robber II	Leetcode

213: run house robber 1 two times with either first house included or the last

20220916

Difficulty	Marks	Name	link
🟠	✅❗❓❌	322. Coin Change	Leetcode

20220923

Diff	Marks	Name	link
🟠	✅❗	743. Network Delay Time	Leetcode
🟠	✅	209. Minimum Size Subarray Sum	Leetcode
🟠	✅❗❓❌		Leetcode
🟠	✅❗❓❌		Leetcode
🟠	✅❗❓❌		Leetcode
🟢	✅❗❓❌		Leetcode
🟢	✅❗❓❌	977. Squares of a Sorted Array	Leetcode
🔴	✅❗❓❌		Leetcode

209: sliding window (left/right pointers)

202209

Diff	Marks	link
🟠	✅❗❓❌	Leetcode
🟠	✅❗❓❌	Leetcode
🟠	✅❗❓❌	Leetcode
🟠	✅❗❓❌	Leetcode
🟢	✅❗❓❌	Leetcode
🔴	✅❗❓❌	Leetcode

Read List

Union-Find/Disjoint Set

TODO:

Quick sort
Quick select
depth first search

Binary search tree

when there are multiple same value (not distinct), how to get the left most index of the given value (or right)
l < r vs l <= r

backtrack / dfs

you can go either way
- starting from position 0, and for each layer down the line you can either add or not add the next element (Leetcode_46), or
- starting form all the element including, you can have any many children as the element, and for each child, consider the corresponding element removed (Leetcode_90)

References:

LeetCode Top 100 Problem Selection | Step-by-step Data Science
GitHub - youngyangyang04/leetcode-master: 🚀 《代码随想录》LeetCode 刷题攻略：200道经典题目刷题顺序
LABULADONG 的算法网站

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README.md		README.md
build.gradle.kts		build.gradle.kts
gradle.properties		gradle.properties
gradlew		gradlew
gradlew.bat		gradlew.bat
settings.gradle.kts		settings.gradle.kts

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Markers:

Difficulties:

Kotlin

Read List

TODO:

Binary search tree

backtrack / dfs

References:

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