Cosine's Landing o7

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Coding Questions

25/05/2025

Leetcode question 2131. Longest Palindrome by Concatenating Two Letter Words

Solution

Editorial
Interesting question. One edge case to handle are duplicate letters in the pair which is doable by having a seperate case. Can sort the string to find duplicates. Had an error with my multiplication though.

24/05/2025

Leetcode question 2942. Find Words Containing Character

Solution

Editorial
Simple question just use contains on the string or iterate through the string.

23/05/2025

Leetcode question 3068. Find the Maximum Sum of Node Values

Solution

Editorial
Interesting question. First instinct was to DP but after realising that there are certain conditions such as having an even number of flips across the tree it becomes easier.

22/05/2025

Leetcode question 3362. Zero Array Transformation III

Solution

Editorial
The trick is to iterate on the numbers array. In doing so you ensure you find the minimum amount of queries possible for a given value with the maximum range. Usint pqs helps but you need to use checks to ensure whether it is possible.

21/05/2025

Leetcode question 73. Set Matrix Zeroes

Solution

Editorial
Initial thought was if a value was 0, set all values in its column and row to 0 however this is too slow. i.e. multiple 0s in a row or column. To speed this up cache the 0 indexes and iterate through the cached 0s without duplicates and set those columns and rows to 0.

20/05/2025

Leetcode question 3355. Zero Array Transformation I

Solution

Editorial
Question is a matter of caching the increment and decrement ranges and then doing 1 parse on the nums array.

19/05/2025

Leetcode question 3024. Type of Triangle

Solution

Editorial
Very easy question. Only tricky part is that if the sum of 2 lengths is less then the third it cannot be a triangle.

Codeforces Contest 2109

A
- Solution
  
  Editorial
  There are 2 situations where it is not true. For every set of numbers, at least 1 person must lose and for each pair of people at least 1 person must win.
B
- Solution
  
  Editorial
  In a 2D plane, we can either initially cut the x or y from the starting position. Initially thought of doing complex mathematics to do it but realised I could do them individually and compare the result.
C
- Solution
  
  Editorial
  Weird question........ Idk look at the official editorial.

18/05/2025

Leetcode question 1931. Painting a Grid With Three Different Colors

Solution

Editorial
DP with bitwise operations and masks. A little annoying to get the checks working and I did the DP wrong. One optimisation is caching the valid candidates for sets of 5 colours which was necessary as my code was slow. I guess you could also cache the valid combinations which will cut down the number of operations by a decent amount but this solution works.

17/05/2025

Leetcode question 75. Sort Colors

Solution

Editorial
Simplest solution is a counting sort as there are only 3 possible values.

16/05/2025

Leetcode question 2901. Longest Unequal Adjacent Groups Subsequence II

Solution

15/05/2025

Leetcode question 2900. Longest Unequal Adjacent Groups Subsequence I

Solution

13/05/2025

Leetcode question 3335. Total Characters in String After Transformations I

Solution

12/05/2025

Leetcode question 2094. Finding 3-Digit Even Numbers

Solution

11/05/2025

Leetcode question 1550. Three Consecutive Odds

Solution

Codeforces Contest 2102

8/05/2025

Leetcode question 3342. Find Minimum Time to Reach Last Room II

Solution

7/05/2025

Leetcode question 3341. Find Minimum Time to Reach Last Room I

Solution

6/05/2025

Leetcode question 1920. Build Array from Permutation

Solution

5/05/2025

Leetcode question 790. Domino and Tromino Tiling

Solution

4/05/2025

Leetcode question 1128. Number of Equivalent Domino Pairs

Solution

Codeforces Contest 2103

A + B (21/04/2025)
C
- Solution
- Personal notes in document.

3/05/2025

Leetcode question 1007. Minimum Domino Rotations For Equal Row

Solution

2/05/2025

Leetcode question 838. Push Dominoes

Solution

30/04/2025

Leetcode question 1295. Find Numbers with Even Number of Digits

Solution

27/04/2025

Leetcode question 3392. Count Subarrays of Length Three With a Condition

Solution

23/04/2025

Leetcode question 1399. Count Largest Group

Solution

21/04/2025

Leetcode question 2145. Count the Hidden Sequences

Solution

Codeforces Contest 2103

A
- Solution
B
- Solution

20/04/2025

Leetcode question 781. Rabbits in Forest

Solution

Codeforces Contest 2096

A
- Solution
B
- Solution

17/04/2025

Leetcode question 2176. Count Equal and Divisible Pairs in an Array

Solution

14/04/2025

Leetcode question 1534. Count Good Triplets

Solution

13/04/2025

Leetcode question 1922. Count Good Numbers

Solution

Codeforces Contest 2093

9/04/2025

Leetcode question 3375. Minimum Operations to Make Array Values Equal to K

Solution

8/04/2025

Leetcode question 3396. Minimum Number of Operations to Make Elements in Array Distinct

Solution

2/04/2025

Leetcode question 2873. Maximum Value of an Ordered Triplet I

Solution

1/04/2025

Leetcode question 2140. Solving Questions With Brainpower

Solution

20/03/2025

Leetcode question 3108. Minimum Cost Walk in Weighted Graph

Solution

19/03/2025

Leetcode question 3191. Minimum Operations to Make Binary Array Elements Equal to One I

Solution

17/03/2025

Leetcode question 2206. Divide Array Into Equal Pairs

Solution

16/03/2025

Leetcode question 2594. Minimum Time to Repair Cars

Solution

15/03/2025

Leetcode question 2560. House Robber IV

Solution

14/03/2025

Leetcode question 2226. Maximum Candies Allocated to K Children

Solution

13/03/2025

Leetcode question 3356. Zero Array Transformation II

Solution

12/03/2025

Leetcode question 2529. Maximum Count of Positive Integer and Negative Integer

Solution

11/03/2025

Leetcode question 1358. Number of Substrings Containing All Three Characters

Solution

Codeforces Contest 2074

05/03/2025

Leetcode question 2579. Count Total Number of Colored Cells

Solution

04/03/2025

Leetcode question 1780. Check if Number is a Sum of Powers of Three

Solution

Codeforces Contest 2067

13/02/2025

Leetcode question 3066. Minimum Operations to Exceed Threshold Value II

Solution

11, 12: Preparation for IMC contest and participation in CPMSOC contest

10/02/2025

Leetcode question 3174. Clear Digits

Solution

09/02/2025

Leetcode question 2364. Count Number of Bad Pairs

Solution

Codeforces Contest 2063

A
- Solution

08/02/2025

Leetcode question 1249. Minimum Remove to Make Valid Parentheses

Solution
Note: Meta OA question

Leetcode question 2349. Design a Number Container System

Solution

07/02/2025

Leetcode question 3160. Find the Number of Distinct Colors Among the Balls

Solution

06/02/2025

Leetcode question 1726. Tuple with Same Product

Solution

Codeforces Contest 2062

A
- Solution
B
- Solution

05/02/2025

Leetcode question 1790. Check if One String Swap Can Make Strings Equal

Solution

04/02/2025

Leetcode question 1800. Maximum Ascending Subarray Sum

Solution

03/02/2025

Leetcode question 3105. Longest Strictly Increasing or Strictly Decreasing Subarray

Solution

Codeforces Contest 2059

A
- Solution

02/02/2025

Leetcode question 1752. Check if Array Is Sorted and Rotated

Notes: Suprisingly difficult
Solution

15/1/2025

Leetcode question 2429. Minimize XOR

Solution

14/1/2025

Leetcode question 2657. Find the Prefix Common Array of Two Arrays

Solution

13/1/2025

Leetcode question 3223. Minimum Length of String After Operations

Solution

12/1/2025

Leetcode question 2116. Check if a Parentheses String Can Be Valid

Kind of difficult and interesting question.
Solution

11/1/2025

Leetcode question 1400. Construct K Palindrome Strings

Solution

10/1/2025

Leetcode question 916. Word Subsets

Solution

9/1/2025

Leetcode question 2185. Counting Words With a Given Prefix

Solution

Codeforces Contest 2057

B
- Solution

8/1/2025

Leetcode question 3042. Count Prefix and Suffix Pairs I

Solution

7/1/2025

Leetcode question 1408. String Matching in an Array

Solution

6/1/2025

Leetcode question 1769. Minimum Number of Operations to Move All Balls to Each Box

Solution

Codeforces Contest 2057

A
- Solution

5/1/2025

Leetcode question 2381. Shifting Letters II

Solution
Interesting problem with char overflow

4/1/2025

Leetcode question 1930. Unique Length-3 Palindromic Subsequences

Solution

3/1/2025

Leetcode question 2270. Number of Ways to Split Array

Solution

Codeforces Contest 2024-2025 ICPC, NERC, Northern Eurasia Finals (Unrated, Online Mirror, ICPC Rules, Teams Preferred)

A
- Solution

2/1/2025

Leetcode question 2559. Count Vowel Strings in Ranges

Solution

30/12/2024

Leetcode question 2466. Count Ways To Build Good Strings

Solution

27/12/2024

Leetcode question 1014. Best Sightseeing Pair

Solution

26/12/2024

Leetcode question 494. Target Sum

Solution

25/12/2024

Leetcode question 515. Find Largest Value in Each Tree Row

Solution

23/12/2024

Advent Of Code Day 4

22/12/2024

Advent Of Code Day 3

Solution A
Solution B
Author’s note: Look at 3B comments. A lot of subfiles were used to make the process easier

21/12/2024

Leetcode question 2872. Maximum Number of K-Divisible Components

Solution

20/12/2024

Advent Of Code Day 19

Advent Of Code Day 1

Advent Of Code Day 2

19/12/2024

Leetcode question 769. Max Chunks To Make Sorted

Solution

17/12/2024

Leetcode question 3264. Final Array State After K Multiplication Operations I

Solution

12/12/2024

Leetcode question 2558 - Take Gifts From the Richest Pile

Solution

Advent Of Code Day 12

Solution A

10/12/2024

Leetcode question 2981 - Find Longest Special Substring That Occurs Thrice II

Solution

09/12/2024

Leetcode question 3152 - Special Array II

Solution

Codeforces Contest 992

A
- Solution
B
- Solution

08/12/2024

Leetcode question 2054 - Two Best Non-Overlapping Events

Solution