I have conducted hundreds of interviews. I noticed very often, the candidate could successfully identify the problem by using a graph approach, but failed to implement the algorithm. In this post, I will discuss the common types of graph algorithms, along with their sample code. Standard DFS (pre-order and post-order) …

Binary Search is a very common algorithm to find a target value in a sorted list. The concept is easy to understand. However, the implementation can be confusing, especially with all the different scenarios: Binary search in a unique sorted list. Binary search in a sorted list with duplicates, and…

I have noticed that my followers and reading stats have been increasing rapidly since I started writing leetcode posts. I really appreciate the support and the interests from you guys! As a current senior software engineer without a degree in computer science, I have spent a lot of time learning…

In this post, we are going to discuss leetcode 1066 — Campus Bikes II, which is asked in Google interviews. Problem Analysis On a campus represented as a 2D grid, there are n workers and m bikes, with n <= m. Each worker and bike is a 2D coordinate on this grid. …

In this post, we are going to discuss leetcode 560 — Subarray Sum Equals K, which is asked in Google, Meta, and Microsoft interviews. Problem Analysis Given an array of integers nums and an integer k, return the total number of subarrays whose sum equals to k. Example 1: Input: nums =…

In this post, we are going to discuss leetcode 1074 — Number of Submatrices That Sum to Target, which is asked in Google interviews. Problem Analysis Given a matrix and a target, return the number of non-empty submatrices that sum to target. A submatrix x1, y1, x2, y2 is the set of…

In this post, we are going to discuss leetcode 1087 — Brace Expansion, which is asked in Google and Amazon interviews. Problem Analysis You are given a string s representing a list of words. Each letter in the word has one or more options. If there is one option, the letter is…

In this post, we are going to discuss leetcode 1091 — Shortest Path in Binary Matrix, which is asked in Google, Meta, Microsoft, and Amazon interviews. Problem Analysis Given an n x n binary matrix grid, return the length of the shortest clear path in the matrix. …

In this post, we are going to discuss leetcode 1096 — Brace Expansion II, which is asked in Google interviews. Problem Analysis Under the grammar given below, strings can represent a set of lowercase words. Let R(expr) denote the set of words the expression represents. The grammar can best be understood through…