Day 22, both parts.

22/22-1.py

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+#!/usr/bin/python3
+
+import collections
+import sys
+
+grid = collections.defaultdict(lambda: collections.defaultdict(bool))
+
+x_moves = [0, 1, 0, -1]
+y_moves = [-1, 0, 1, 0]
+
+with open(sys.argv[1]) as input_file:
+    linenum = 0
+    for line in [l.rstrip() for l in input_file]:
+        infected = [c == '#' for c in list(line)]
+        offset = (len(infected) - 1) // 2
+        for i in range(0, len(infected)):
+            grid[linenum - offset][i - offset] = infected[i]
+        linenum += 1
+
+x = 0
+y = 0
+direction = 0
+
+counts = collections.defaultdict(int)
+
+for step in range(0, 10000):
+    dir_change = 1 if grid[y][x] else -1
+    direction = (direction + dir_change) % 4
+
+    counts[grid[y][x]] += 1
+    grid[y][x] = not grid[y][x]
+
+    x += x_moves[direction]
+    y += y_moves[direction]
+
+print(counts)

22/22-2.py

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+#!/usr/bin/python3
+
+import collections
+import sys
+
+grid = collections.defaultdict(lambda: collections.defaultdict(int))
+
+x_moves = [0, 1, 0, -1]
+y_moves = [-1, 0, 1, 0]
+
+with open(sys.argv[1]) as input_file:
+    linenum = 0
+    for line in [l.rstrip() for l in input_file]:
+        infected = [2 if c == '#' else 0 for c in list(line)]
+        offset = (len(infected) - 1) // 2
+        for i in range(0, len(infected)):
+            grid[linenum - offset][i - offset] = infected[i]
+        linenum += 1
+
+x = 0
+y = 0
+direction = 0
+
+counts = collections.defaultdict(int)
+
+for step in range(0, 10000000):
+    dir_change = grid[y][x] - 1
+    direction = (direction + dir_change) % 4
+
+    counts[grid[y][x]] += 1
+    grid[y][x] = (grid[y][x] + 1) % 4
+
+    x += x_moves[direction]
+    y += y_moves[direction]
+
+print(counts)

22/testcase.txt

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+.........
+.........
+.........
+.....#...
+...#.....
+.........
+.........
+.........
+.........