Check out my new course Learn you some Lambda best practice for great good! and learn the best practices for performance, cost, security, resilience, observability and scalability.
This is a more difficult version of problem 82, and now you can move in all four directions!
As before, we start by loading the input data into a 2D array:
and initialize another matrix of the same size to hold the minimum sum leading to each cell:
What we have done differently this time though, is to choose initial defaults:
- for the top-left corner (0, 0) the minimum sum is itself
- for all other cells at (row, col) we’ll always traverse right and then down
- if row = 0, then this equates to only move right until we reach col
- if col = 0, then this equates to only move down until we reach row
Next, as we did for the problem 82, we’ll add a couple of helper to help us traverse both matrices:
and we’ll find the new minimum sum to each cell by taking the minimum from the four directions:
Unlike before, we can’t isolate to optimizing one column at a time, and instead we’ll need to traverse the whole matrix. For better cache locality, we’ll traverse row first and recursively optimize the whole matrix until no more optimization is possible:
Finally, find the final value for the bottom-right corner of the sum matrix:
This solution runs in 73ms on my laptop.
The source code for this solution is here.
I specialise in rapidly transitioning teams to serverless and building production-ready services on AWS.
Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.
Check out my new course, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. Enrol now and enjoy a special preorder price of £9.99 (~$13).
Are you working with Serverless and looking for expert training to level-up your skills? Or are you looking for a solid foundation to start from? Look no further, register for my Production-Ready Serverless workshop to learn how to build production-grade Serverless applications!
Here is a complete list of all my posts on serverless and AWS Lambda. In the meantime, here are a few of my most popular blog posts.
- Lambda optimization tip – enable HTTP keep-alive
- You are thinking about serverless costs all wrong
- Many faced threats to Serverless security
- We can do better than percentile latencies
- I’m afraid you’re thinking about AWS Lambda cold starts all wrong
- Yubl’s road to Serverless
- AWS Lambda – should you have few monolithic functions or many single-purposed functions?
- AWS Lambda – compare coldstart time with different languages, memory and code sizes
- Guys, we’re doing pagination wrong