Post: Advent of code day 6

posts/adventofcode/2017/06-memory-reallocation.md

@@ -0,0 +1,64 @@
+---
+title: "Memory Reallocation — Python — #adventofcode Day 6"
+description: "In which I relive a programming exercise from my masters course."
+slug: day-06
+date: 2017-12-09T17:45:46+00:00
+tags:
+- Technology
+- Learning
+- Advent of Code
+- Python
+series: aoc2017
+---
+
+[Today's challenge](http://adventofcode.com/2017/day/6) asks us to follow a recipe for redistributing objects in memory that bears a striking resemblance to the rules of the African game [Mancala](http://en.wikipedia.org/wiki/Mancala).
+
+!!! 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](http://en.wikipedia.org/wiki/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!
+
+```python
+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)
+```