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Coding Questions

30/09/2025

Leetcode question 2221. Find Triangular Sum of an Array

Solution

Editorial
Compute each sub layer then return when the layer size is 1.

28/09/2025

Leetcode question 976. Largest Perimeter Triangle

Solution

Editorial
Sort the points then iterate through all triplets adjacent to each other.

27/09/2025

Leetcode question 812. Largest Triangle Area

Solution

Editorial
Iterate through all pairs of points and ensure they are valid then call the max_area.

25/09/2025

Leetcode question 120. Triangle

Solution

Editorial
2D dp. 2 possible child nodes for each element in the tree. Went up the triangle to reduce end computations.

9/09/2025

Leetcode question 2327. Number of People Aware of a Secret

Solution

Editorial
2D dp. Annoying part is doing forget and sharing. The bounds of the two are a bit finnicky.

7/09/2025

Leetcode question 1304. Find N Unique Integers Sum up to Zero

Solution

Editorial
Insert n - 1 unique numbers then insert the negative.

5/09/2025

Leetcode question 1584. Min Cost to Connect All Points

Solution

Editorial
Find the mst of the points after computing edge weights.

Leetcode question 990. Satisfiability of Equality Equations

Solution

Editorial
Find DSU of the equality tree then check the inequalities.

4/09/2025

Leetcode question 146. LRU Cache

Solution

Editorial
Uses maps and linked lists. Refer to lists in std lib.

Leetcode question 3516. Find Closest Person

Solution

Editorial
Stock standard absolute value check and difference.

2/09/2025

Leetcode question 3025. Find the Number of Ways to Place People I

Solution

Editorial
Some checks whether the pair is valid then if every node is outside. O(n^3) time is brute forceable.

Codeforces Contest 2132

A
- Solution
  
  Editorial
  This question was append or prepend to a string depending on v and d.
B
- Solution
  
  Editorial
  The question was to determine if the number was divisible by a value 10^x + 1 and store them.
C1
- Solution
  
  Editorial
  The minimum amount of orders is determining the remainder mod 3^x for all x and summing them together.
C2
- Solution
  
  Editorial
  For any combination, breaking an order into 3 smaller orders is cheaper. Thus we need to determine the minimum number of orders then break larger orders into smaller depending on how many orders are available.
E
- Solution
  
  Editorial
  Interesting question. Required to use the hints. Initial thoughts was decreasing values and dual graphs and summation of the two graphs. However because it is not a linear function we can not binary search. After looking at the solutions I realised the main problem was that I was trying to work from a base set of values then expand. The solution was to overestimate x and y then decrease them to fit the limit.

1/09/2025

Leetcode question 1792. Maximum Average Pass Ratio

Solution

Editorial
Greedy with max heap properties. Proof would be for any combination of extra students. Put them where it will increase the ratio the most. For any other deviation from the optimal, the return of ratio increase would be worst.

30/08/2025

Leetcode question 36. Valid Sudoku

Solution

Editorial
Check first rows, then columns then the subsquares.

29/08/2025

Leetcode question 3021. Alice and Bob Playing Flower Game

Solution

Editorial
The pair is valid if the sum of flowers is odd. So count the number of odds pairs for any combination of n and m. Which can be done with some modulus and maths.

28/08/2025

Leetcode question 3446. Sort Matrix by Diagonals

Solution

Editorial
Break it down into 2 sets and get the numbers, sort them then reinsert

Codeforces Contest 2136

A
- Solution
  
  Editorial
  The answer is to ensure that for any given half, a team's score for the half is not greater then a value (as shown in the code).
B
- Solution
  
  Editorial
  Sliding window question. If for any string of length k, there is no '0' then at least one of them must be maximum and thus it would be invalid.
C
- Solution
  
  Editorial
  Using a map, a queue and a best_so_far, we can use DP to determine whether using a new neat array is better or worse then not using it.

26/08/2025

Leetcode question 3000. Maximum Area of Longest Diagonal Rectangle

Solution

Editorial
Eval the max value and swap if it is greater

Codeforces Contest 2134

A
- Solution
  
  Editorial
  Modulus check on the numbers and coverage check.
B
- Solution
  
  Editorial
  Was a modulus check in mod k + 1. Each addition decreases the remainder of mod k + 1 by 1.
C
- Solution
  
  Editorial
  2 things are important. The predecessor and successor at event indices. Greedy so you make the predecessor legal when compared to the current and then the successor legal when comparing the current by the succ and pred.

24/08/2025

Leetcode question 1493. Longest Subarray of 1’s After Deleting One Element

Solution

Editorial
Predecessors and successors counting. Edge case encountered where the index 0 or last element is deleted. Also made errors in my own code on how it should work.

Codeforces Contest 2133

A
- Solution
  
  Editorial
  Check if two numbers are the same.
B
- Solution
  
  Editorial
  Sort decreasing then sum every odd number.
C
- Solution
  
  Editorial
  Weird question which required topological ordering, path lengths then adjacency checks. First find the longest paths, then check for valid next nodes with length minus 1.

Codeforces Contest 2034

A
- Solution
- https://www.youtube.com/watch?v=XZSsTcJzayc
  
  Editorial
  This is a question to find the LCM of the two numbers.
B
- Solution
- https://www.youtube.com/watch?v=k5cUNLMUClQ
  
  Editorial
  Need a check on whether the last x where 0 which could be done iteratively then solve from there

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.