Leetcode C# solution and notes

I will use this repository to make notes for leetcode solutions and classify the problems by different topics.

Solved Problem List

Total solved: 108

microsoft-labed

top-interview-questions

Algorithms Basics

First, I will start from the very basic and useful part. The Leetcode Course Section, which is selected interview questions aimed for beginners who do not know algorithms or need a refresher. Learn by doing.

Chapter 1. Array / String (with similar problem)

Chapter 2. Linked List (with similar problem)

Chapter 3. Binary Tree

Chapter 4. Stack and Queue

Chapter 5. Bit Manipulation

Chapter 6. Binary Search

Other Topics

Sorting

Palindrome

All the Palindrome problem's core solution is check if reverse == origin. A efficient way is to compare reverse the sencond half, and check if FirstHalf(origin) == SecondHalf(reversed). For int, core solution is:

while (x > rev) {
    rev = rev * 10 + x % 10;
    x = x / 10;
}
return (x == rev || x == rev / 10);

For string, core solution is:

while (left <= right){
    if (char.ToLower(leftChar) 
        != char.ToLower(rightChar)){
        return false;
    }
    left++;
    right--;
}
return true;

SubString Topic

13. Roman to Integer

Common knowledge

Symbol | I | V | X | L | C | D | M Value | 1 | 5 | 10 | 50 | 100 | 500 | 1000

I placed before V or X indicates one less, so IV is 4 (5 - 1) and IX is 9 (10 - 9)

X placed before L or C indicates ten less, so XL is 40 (50 - 10) and XC is 90 (100 - 10)

C placed before D or M indicates a hundred less, so four hundred is CD (a hundred less than five hundred) and nine hundred is CM (a hundred less than a thousand)