Day 22

22.py

@@ -0,0 +1,64 @@
+#!/usr/bin/python3
+
+"""Solution for day 22 of Advent of Code 2016.
+
+Part 1 is straight-forward reading of the data, generating pairs using itertools.permutations, and counting how
+many match the criteria.
+
+As is traditional at about this point in Advent of Code, part 2 requires you to make annoying assumptions based on
+the vague example in the question and some properties of your input that you have no guarantee are universal.
+
+In this case, the input needs to be partitioned in to three sets: empty nodes (of which there is just one), giant
+nodes (whose data can't possibly be placed anywhere else) and normal nodes (who can shift their data to the empty
+node, but not to any other normal node).
+
+When the nodes are printed out according to their type (as in the example), it becomes obvious that there's a "wall"
+of giant nodes in the way. As the only valid moves involve the empty node, you basically have to move that around and
+use it to move the data along the top row.
+
+For my input, it takes 34 moves to rearrange things and then move the target data left by one:
+
+..............23456789012345678901234
+..............1......................
+..............0######################
+..............9876543................
+....................2................
+....................1................
+...................._................
+.....................................
+.....................................
+
+Then for each node to the left it takes an additional five moves, as the empty space loops around our target:
+
+....45_..
+....321..
+.........
+
+It needs to move a total of 35 nodes left, so 34+35*5 total moves = 209.
+"""
+
+import re
+
+import itertools
+
+matcher = re.compile(r'^/dev/grid/node-x([0-9]+)-y([0-9]+)\s+([0-9]+)T\s+([0-9]+)T\s+([0-9]+)T\s+.*$')
+
+# Constants used for convenient access the groups in the matcher above
+locx = 0
+locy = 1
+size = 2
+used = 3
+free = 4
+
+with open('data/22.txt', 'r') as data:
+    discs = [tuple(map(int, matcher.match(l).groups())) for l in data.readlines() if matcher.match(l)]
+    pairs = sum(1 for p in itertools.permutations(discs, 2) if 0 < p[0][used] <= p[1][free])
+    print('Part one: %s' % pairs)
+
+    print('Part two: ...')
+    grid = dict((disc[:locy+1], disc) for disc in discs)
+    for y in range(27):
+        print(''.join(['X' if (x,y) not in grid
+                       else '_' if grid[(x, y)][used] == 0
+                       else '#' if grid[(x, y)][used] > 150  # Arbitrary cut-off for "normal" vs "giant" nodes
+                       else '.' for x in range(37)]))