Quicksort is one of the most efficient sorting algorithm with O(log n) Big-O notation. It can be 2x – 3x faster than merge sort. It is another divide-and-conquer algorithm. The algorithm divides the list on a pivot, which can be any number in the list. Any item lower than the pivot is added to a ‘left’ list. Any item larger than the pivot is added to the ‘right’ list. The process is repeated recursively with any sub-list with more than 2 items.

Continue reading# Algorithms

# Merge Sort Aglorithm

I mentioned in yesterday’s post that a lot of data manipulation involves lists, nested and otherwise. Another common task is sorting elements in a list. Day 6 of 30 Days of Algorithms is a Merge Sort, which is another “divide-and-conquer” algorithm.

Continue reading# Array to Tree Algorithm

Managing data almost always involves working with hierarchical or nested data. Whether we are talking about nested files and folders, product categories and sub-categories, music, … you name it. But we store data in a database in a flat structure. This makes sense because the data objects themselves share the same attributes and it makes for easy searching. But how we store the data and how we need to visualize and manipulate it don’t necessarily match. So how do we efficiently transform a flat array to a tree? Day 5 of 30 Days of Algorithms will present one solution with *O(n)* complexity.

# List Intersection / List Overlap Algorithm

Given two lists of elements, how do you find which items appear in both lists? The algorithm for Day 4 of 30 Days of Algorithms demonstrates how to find the overlap of two lists (list intersection).

Continue reading# Bubble Sort Algorithm

Our algorithm for Day 3 of 30 Days of Algorithms is a Bubble Sort. Bubble Sort is not an efficient sort algorithm (The Big-O notation for the time complexity is *0n ^{2}*) but it is useful for learning. The basic premise is very simple : Start with the first two items in the list. If the first item (left) is higher than the second item (right), swap them.

# Find Missing Number Algorithm

The algorithm for Day 2 of 30 Days of Algorithms is a useful formula to find a missing number in an array of numbers from 1 – N. This algorithm only works if there is one-and-only-one missing number, and no duplicate numbers. There are other algorithms for those cases which I will cover on a different day.

Continue reading# Euclid’s Algorithm for Greatest Common Divisor

Euclid’s algorithm finds the largest number that divides evenly into two numbers – the greatest common divisor (GCD). The Greek mathematician Euclid published the algorithm in his work, Elements in 300 BC.

Continue reading# 30 Days of Algorithms in JavaScript

I recently decided to re-enter the “real world” after freelancing for three years. My very first interview was at InVision. It did not go well, to say the least. The coding test focused on common algorithms in JavaScript, and I bombed. After receiving the polite rejection email, I asked the recruiter for feedback from the hiring team so I could improve.

Continue reading