I wrote up a gist for last week’s Riddler Express, including the extra credit, but forgot to link it here, probably because I was on holiday! Anyway, this week’s Classic looked very tractable.

# Blogs as Unfakeable Commitments

Some will say that you should keep a blog to demonstrate expertise, or to get practice in writing, or to engage with others in your area. I think there’s another reason that doesn’t get mentioned much: blogging is an unfakeable signal of commitment.

# Riddler Express, August 28 2020

I didn’t add last week’s Classic to this blog, but I did produce a pretty graph in Jupyter from which you can read the right answer (in either graph, the point on the x-axis where the orange four-post line first exceeds the blue three-post line.)

This week’s Express is not difficult, but I did find the answer a little surprising.

# Buying a Flat in Poland – What I Needed

I’m doing this, with my girlfriend. I have bought a place in the UK before, but other people handled all of the paperwork in that case. So my initial expectations were for something like the UK system, but the reality was a little different. We haven’t finished yet, but this post is an outline of the important differences I saw.

# Riddler Classic, August 14 2020

I did this one analytically and by brute force simulation, and got the same answer with both methods. It’s in a github gist.

# Riddler Express, July 24 2020

Got the Classic from two weeks ago correct, although I hadn’t got the closed-form solution; I needed to spend more time playing with toy examples, but I’m not sure I would have discerned the pattern anyway. It’s neat though.

This week’s Express is not too difficult (*please don’t let me get it wrong!*). The thing that surprised me on thinking about it is that the total number of combinations of shires is only 1024. That’s 2^{10}, since there are 10 shires, each of which can be in or out of any particular subset.

Half of the possibles combinations of shires don’t have enough votes to win, and of those combinations that do, many of them could lose a shire and still win, so they can be ignored as well.

My 33 lines of code will print out an answer in about a millisecond. I assume in Haskell it could be done in about four lines! I should take a look at that language sometime.

# Riddler Classic, July 10 2020

My answer last week seems to be wrong; I thought agreeing with LL would be enough. I will need to look more closely at it.

This week’s Classic is about stacking blocks. At first glance I thought it was Tower of Hanoi, but it’s a little different:

# Riddler Classic, July 3 2020

Got last week’s Express just right, with the right explanation.

This week’s Classic is based on the US flag, but the maths question is this:

[W]hen

Nequals 50,Nis twice a square andN+1 is a centered pentagonal number. After 50, what is the next integerNwith these properties?

# Riddler Express, June 26 2020

Simple question for this one:

In Riddler City, the city streets follow a grid layout, running north-south and east-west. You’re driving north when you decide to play a little game. Every time you reach an intersection, you randomly turn left or right, each with a 50 percent chance.

After driving through 10 intersections, what is the probability that you are still driving north?