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C'est la Z

It gets easier (or advent of code 2016 day 19)

Today's Advent of Code problem was a variant on the Josephus problem.

I recalled that there was a formula to figure out the sole survivor but I decide to run a simulation rather than looking it up. I also decided to write it up in C++, well, really C with cout instead of printf.

Part 1 was the traditional problem. Part 2 was a variant where at each iteration, you remove the elf opposite the elf being processed (see the problem description for details).

For both solutions I coded up a circular doubly linked list:

struct node *make_ring(int size){
int i;
struct node *n;
struct node *current,*first;

first = (struct node *)malloc(sizeof(struct node));

for  (i=0;i<size-1;i++){
n=(struct node *)malloc(sizeof(struct node));

return first;


You can see my complete solutions here.

I was thinking about how I wrote the code – I just rolled it off the top of my head. The same was true for the earlier AoC problems where I had to implement a breadth first search or something similar.

I'm not making a statement about my amazing coding abilities - linked lists and graph searches are pretty basic, but rather than having done the CS thing for so long, these fundamentals have become somewhat routine. I haven't really written C code in years but other than a couple of typos (and a stupid mistake in calculating steps) things worked right off the bat.

I remember a time when I was in college or even a young professional when I would use an array and an index as a stack or queue - not because it made more sense but rather, because I wasn't fully comfortable with memory manipulation and linked lists. The same could be said for my first few years working with anything more than the simplest recursion.

All of this is to say that it does get easier.

Things that seem trivial to us now seemed insurmountable when we were beginners. Last year, I wrote about an overnight homework assignment I gave to my class that would have been a final project a year earlier (the post is here but the homework links are no longer active) and a few weeks ago I recall a fellow CS teacher talking about how much longer it takes his students to write a chunk of code than it takes the teacher.

New things are challenging and take time but with practice and persistence techniques that were once daunting can become tools ready at our disposal to use on a whim.

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