erambler/content/post/adventofcode/2017/06-memory-reallocation.md

title	description	slug	date	tags	series
Memory Reallocation — Python — #adventofcode Day 6	In which I relive a programming exercise from my masters course.	day-06	2017-12-09T17:45:46+00:00	Technology Learning Advent of Code Python	aoc2017

Today's challenge asks us to follow a recipe for redistributing objects in memory that bears a striking resemblance to the rules of the African game Mancala.

→ Full code on GitHub

!!! commentary When I was doing my MSci, one of our programming exercises was to write (in Haskell, IIRC) a program to play a Mancala variant called Oware, so this had a nice ring of nostalgia.

Back to Python today: it's already become clear that it's by far my most fluent language, which makes sense as it's the only one I've used consistently since my schooldays. I'm a bit behind on the blog posts, so you get this one without any explanation, for now at least!

import math


def reallocate(mem):
    max_val = -math.inf
    size = len(mem)
    for i, x in enumerate(mem):
        if x > max_val:
            max_val = x
            max_index = i

    i = max_index
    mem[i] = 0
    remaining = max_val

    while remaining > 0:
        i = (i + 1) % size
        mem[i] += 1
        remaining -= 1

    return mem


def detect_cycle(mem):
    mem = list(mem)
    steps = 0
    prev_states = {}

    while tuple(mem) not in prev_states:
        prev_states[tuple(mem)] = steps
        steps += 1
        mem = reallocate(mem)

    return (steps, steps - prev_states[tuple(mem)])


initial_state = map(int, input().split())

print("Initial state is ", initial_state)
steps, cycle = detect_cycle(initial_state)
print("Steps to cycle: ", steps)
print("Steps in cycle: ", cycle)