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Phoenix, AZ /

Practice coding challenges Part 2 - Intermediate-to-advanced level

DevMountain | Phoenix 4600 E Washington St , Phoenix, AZ 85034 (map)

Logistical details:

This group moved to DevMountain at 4600 E Washington St, Phoenix, AZ 85034

If you get stuck outside please call me at (623)[masked].


Note: You need to bring your own computer for this meetup.

Another Note: In this group I often recommend that you use free online services to practice coding challenges. But not everyone wants to give out their email. In case you don't want to give your email to LeetCode, Hackerrank, FreeCodeCamp, etc., one option is to make a throwaway email account on 10 Minute Mail. If you use a throwaway email, you should be able to submit your code and see if it passes the test cases without getting unwanted emails.

Also please note that I'm not a teacher, just a person who knows JavaScript, Java, and Python and likes to talk about coding, so this is not a class, it is supposed to be simply a conversation in a supportive environment. The problems I've chosen for this group are basically at the limit of where my abilities are at this time.

Before the meetup happens I will update this description with some code challenges that we can work on. Ideally we will discuss our approach, talk about efficiency, and generally help each other out. There is a projector so we can share our code with the classroom.


The theme for July 7 is Union Find. For these problems you have to keep track of which nodes in a graph are connected to the same cluster. This topic comes from Week 1 of Princeton's free Algorithms course on Coursera ( and there are some explanatory videos and slides there.



The third problem for today is from the Coursera course (the equivalent problem is on Leetcode but behind a paywall):

"Given a social network containing n members and a log file containing m timestamps at which times pairs of members formed friendships, design an algorithm to determine the earliest time at which all members are connected (i.e., every member is a friend of a friend of a friend ... of a friend). Assume that the log file is sorted by timestamp and that friendship is an equivalence relation. The running time of your algorithm should be m log ⁡n or better and use extra space proportional to n."


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