Posts | Marc Lester Tan

Presentations (2)

Presentation (1)

Posts

158 posts

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Jul 8, 2020
One minute read

For this problem, the approach is really straightforward, just add 1 to each of the digit and making sure that the carry is considered as well. ...

Binary Tree Level Order Traversal II

Jul 2, 2020
2 minutes read

Today, we’re going to solve a variation of the Binary Tree Level Order Traversal. ...

Arranging Coins

Jul 1, 2020
3 minutes read

For the month of July, I decided to get back onto "Leetcoding" after almost 2 weeks of hiatus from solving algorithmic problems. Every month since April this year, Leetcode organizes this 30-day challenge where each day, you have to solve 1 problem. For today, we are going to solve a problem called "Arranging Coins". ...

Making Safe Functions

Jun 26, 2020
2 minutes read

When we write Kotlin functions, it’s important that we make sure that our code is stable and behave correctly. It’s also important to be clear as to what the function expects in order to behave correctly. ...

Jun 26, 2020
One minute read

It’s been more than a week since I got the result of a 1-year long preparation and I can still feel the excitement, disbelief and nirvana all throughout my body :). I will share more details about it in the upcoming days. ...

Range Sum Query 2D

Feb 27, 2020
2 minutes read

Here’s a hard LC problem which is actually just a variation of the Range Sum Query problem but instead, you have to work on a 2D data. ...

Binary Index Tree

Filling Bookcase Shelves

Feb 16, 2020
2 minutes read

Another medium LC problem in which we are asked to arrange the books in a bookshelf with certain width and try to minimize the total height of the books after the arrangement. ...

Dynamic Programming

Largest Values From Labels

Feb 16, 2020
2 minutes read

For this medium LC problem, I’m presenting two variations of my solution: Using array and another using PriorityQueue. ...

Shortest Distance to Target Color

Feb 13, 2020
2 minutes read

The solution here for this medium LC problem might not be the fastest but I think it’s really clean and concise and easy to understand. ...

Alphabet Board Path

Feb 13, 2020
2 minutes read

It took me about 20 minutes to think about the solution for this medium LC problem and just few minutes to actually implement the code. ...

Brace Expansion II

Feb 13, 2020
One minute read

This is a follow-up question for the Brace Expansion problem earlier and the only difference is that now, the braces can be nested multiple times. ...

Brace Expansion

Feb 13, 2020
One minute read

This medium LC problem asks us to return all the words formed by expanding the characters inside the braces and appending it to all the other characters present in the string. ...

Contain All Alphabet

Feb 12, 2020
2 minutes read

Recently, somebody posted a problem that was asked in his Google Phone Interview. The first problem was easy and could be solved with an O(n) algorithm. 1. Find out if a string contains all alphabet characters in their respective order. ...

Redundant Connection

Feb 9, 2020
2 minutes read

This medium LC problem is about finding the edge which causes the tree to have a cycle. ...

Connecting Cities With Minimum Cost

Feb 9, 2020
2 minutes read

This medium LC problem is basically a minimum spanning tree problem therefore we can use Kruskal’s algorithm to solve it. ...

Network Delay Time

Feb 9, 2020
2 minutes read

This medium LC question can be solved by using Djikstra algorithm. The goal is to find the individual distances of nodes from a given node. Then, the maximum distance will be the total network delay time. The time complexity for this algorithm is O(NlogN + E), N = number of nodes and E = number of edges. ...

Most Stones Removed With Same Row or Column

Nov 20, 2019
One minute read

This medium LC question is really difficult to solve if you don’t have any background about Disjoint Sets. ...

Campus Bikes II

Oct 26, 2019
One minute read

Here’s a medium (problem)[https://leetcode.com/problems/campus-bikes-ii/] which can be solved by using backtracking. Since the problem mentioned about minimizing the sum of distances for a possible combination of workers and bikes, we can use backtracking to go through all possible combinations of bikes and workers. We also keep track of the minimum sum and use that as the final answer. ...

Range Sum Query Immutable

Oct 23, 2019
2 minutes read

An easy level question with an interesting solution. ...

Character Mapping

Oct 5, 2019
One minute read

This isn’t a solution to a problem but this could be really handy when solving some problems on LC particularly when you need to create a histogram of characters in a particular string. For example, the word “leetcode” will have a histogram of: ...

Oct 4, 2019
One minute read

To solve this problem, you need to know the arithmetic progression formula. ...

Invalid Transactions

Oct 1, 2019
2 minutes read

Starting today, I will try to solve mostly medium level LC questions as I’ve solved about 75% of easy questions. This one seems to be quite easy as it only involves straightforward logic. ...

Sep 30, 2019
One minute read

The solution to this problem is very easy but I struggled a little bit because I was focusing more on finding a regex to represent the pattern. ...

1-Bit and 2-Bit Characters

Sep 29, 2019
One minute read

The idea to solve this problem is to first, get the total number of bits then iterate through each bit and if the previous bit is 1, then deduct 2 from the total number of bits. If it’s a 0, then deduct only 1. In the end, if the total number of bits is equal to 1, then last character must be a 1-bit character. ...

Search in a Sorted Array of Unknown Size

Sep 29, 2019
One minute read

Honestly, this should be an easy-level problem as it only involves binary search. ...

Sep 29, 2019
One minute read

As I’ve mentioned before, I really enjoy solving problems involving bit manipulation and this is one of the many problems that are fun to solve with. ...

Valid Word Square

Sep 29, 2019
One minute read

This is a fun problem to solve and also relatively very easy. I was able to solve this with just one try. ...

Binary Tree Level Order Traversal II

Sep 29, 2019
One minute read

The solution for this problem is the same as the other similarly named problem. Except at the end, we just have to reverse the list before returning it. ...

Minimum Depth of Binary Tree

Sep 29, 2019
One minute read

Here’s another shot at a tree traversal problem. This solution uses Depth-First Traversal. ...

Valid Mountain Array

Sep 29, 2019
One minute read

The idea for this problem is to first find the index of the peak. Peak is defined as A[i-1] < A[i] > A[i+1]. ...

Get Equal Substrings Within Budget

Sep 29, 2019
One minute read

The approach for this problem is to use sliding window technique after getting an array of all the costs involved per character. ...

Sep 28, 2019
2 minutes read

This problem does not support Kotlin yet so I have to do it in Java. ...

Minimum Index Sum of Two Lists

Sep 28, 2019
One minute read

The solution for this problem is to loop through any of the list and each time a word exists in both lists, then get the sum of their indexes and use that as the key to store the word in a hashmap. Also, keep track of the lowest key of the map so that later on, you can use that to return the answer. ...

First Unique Character in a String

Sep 27, 2019
One minute read

Most problems like this one can be solved by using the character count map. This approach is very effective as it can give you O(n) time complexity. ...

Majority Element

Sep 27, 2019
One minute read

Writing code in Kotlin brings so much fun particularly when solving Leetcode problems such as this one. ...

Sep 27, 2019
One minute read

For this problem, the idea is to swap each digit with their corresponding 180-degree values and use Integer.parseInt to verify if it’s still a valid number. If yes, check also if it’s not equal to the original number as this may also affect the validity of the number. ...

Occurrences After Bigram

Sep 27, 2019
One minute read

Another easy one with a straightforward answer. ...

Merge Intervals

Sep 26, 2019
One minute read

This is one of the commonly asked questions in LC as there were about 22 companies who’ve used this question in their interviews. ...

Minimum Absolute Difference

Sep 26, 2019
One minute read

The idea to solve this problem is to sort the input array and then use a sliding window approach to find the minimum absolute difference between two consecutive elements. If we find a new low, then clear the result and add the current elements. Add more elements if the current diff is equal to the lowest diff so far. ...

How Many Apples Can You Put Into the Basket

Sep 26, 2019
One minute read

Straightforward solution for this easy problem ...

Prime Palindrome

Sep 26, 2019
One minute read

This is one tough medium problem and I had to look at the official solution to solve this. I can solve for smaller numbers but once it gets to 7+ digits then I always get the Time Limit Exceeded result. ...

Excel Sheet Column Number

Sep 25, 2019
One minute read

One of the favorite problems in LC because the problem looks simple but the solution involves quite a bit of analysis. ...

Sep 25, 2019
One minute read

The easiest way to solve this problem is to count the number of uppercase character. We can easily do that by using map and Character.isUpperCase functions. ...

Sep 25, 2019
One minute read

I never expect that the solution for this problem would be this easy so here it goes. ...

Roman to Integer

Sep 25, 2019
One minute read

I solved this using Java before so this is just a re-implementation in Kotlin language. ...

Two Sum IV - Input Is a BST

Sep 25, 2019
2 minutes read

This is a fun problem as it really makes you think of how to improve your solution. There are multiple ways of solving this such as iterating through the tree and collecting all the values in a hash set. Then loop through the hash set and find if there are any entry equals to k - current element. ...

Contains-DuplicateII

Sep 24, 2019
One minute read

This is a variation of the previous problem. Again, this is best solved using hashmap. ...

Contains-Duplicate

Sep 24, 2019
One minute read

There are multiple ways to solve this problem. One could sort the arrays and check element by element if two consecutive items are equal. ...

Find the Difference

Sep 23, 2019
One minute read

Just another easy problem. ...

Single Element in a Sorted Array

Sep 23, 2019
2 minutes read

This medium problem can be solved easily by few lines of code with O(n) time complexity. ...