Add day 15, 16, 17, 18, 2016

Author: snhansen

2016/day15/solution.py

@@ -0,0 +1,26 @@
+import re
+from itertools import count
+
+with open("input") as f:
+    inp = f.read().strip()
+
+discs = []
+for line in inp.split("\n"):
+    nums = list(map(int, re.findall("\d+", line)))
+    nums.pop(2)
+    discs.append(tuple(nums))
+
+
+def solve(part2 = False):
+    if part2:
+        discs.append((len(discs) + 1, 11, 0))
+    for t in count():
+        if all((init_pos + t + disc) % n == 0 for disc, n, init_pos in discs):
+            return t
+
+
+# Part 1
+print(solve())
+
+# Part 2
+print(solve(True))

2016/day16/solution.py

@@ -0,0 +1,32 @@
+def process(s):
+    res = ""
+    for c in s[::-1]:
+        bit = "1" if c == "0" else "0"
+        res += bit
+    return s + "0" + res
+
+
+def checksum(s):
+    pairs = []
+    res = ""
+    for i in range(0, len(s), 2):
+        pairs.append(s[i:(i + 2)])
+        x = "1" if s[i] == s[i + 1] else "0"
+        res += x
+    if len(res) % 2 == 1:
+        return res
+    return checksum(res)
+
+
+def solve(length):
+    state = "10111100110001111"
+    while len(state) < length:
+        state = process(state)
+    return checksum(state[:length])
+
+
+# Part 1
+print(solve(272))
+
+# Part 2
+print(solve(35651584))

2016/day17/solution.py

@@ -0,0 +1,36 @@
+import hashlib
+from collections import deque
+
+passcode = "qzthpkfp"
+
+
+def get_dirs(path):
+    dirs = [-1j, 1j, -1, 1]
+    hash_ = hashlib.md5((passcode + path).encode()).hexdigest()
+    hash_ = hash_[:4]
+    return [dirs[i] for i, c in enumerate(hash_[:4]) if "b" <= c <= "f"]
+        
+
+dirs_letter = {1: "R", -1: "L", 1j: "D", -1j: "U"}
+first = True
+longest_path = 0
+q = deque([(0, "")])
+seen = set()
+while q:
+    p, path = q.popleft()
+    if (p, path) in seen:
+        continue
+    if p == 3+3*1j:
+        longest_path = max(longest_path, len(path))
+        if first:
+            print(path)
+            first = False
+        continue
+    seen.add((p, path))
+    for dp in get_dirs(path):
+        new_p = p + dp
+        if not (0 <= new_p.real <= 3 and 0 <= new_p.imag <= 3):
+            continue
+        q.append((new_p, path + dirs_letter[dp]))
+
+print(longest_path)

2016/day18/solution.py

@@ -0,0 +1,36 @@
+with open("input") as f:
+    inp = f.read().strip()
+
+
+def next_row(s):
+    res = ""
+    for i in range(len(s)):
+        if i == 0:
+            tiles = (".", s[0], s[1])
+        elif i == len(s) - 1:
+            tiles = (s[len(s) - 2], s[len(s) - 1], ".")
+        else:
+            tiles = (s[i-1], s[i], s[i+1])
+        left, center, right = tiles
+        if left == "^" and center == "^" and right == ".":
+            res += "^"
+        elif left == "." and center == "^" and right == "^":
+            res += "^"
+        elif left == "^" and center == "." and right == ".":
+            res += "^"
+        elif left == "." and center == "." and right == "^":
+            res += "^"
+        else:
+            res += "."
+    return res
+
+
+rows = [inp]
+for i in range(400000 - 1):
+    rows.append(next_row(rows[-1]))
+
+# Part 1
+print(sum(row.count(".") for row in rows[:40]))
+
+# Part 2
+print(sum(row.count(".") for row in rows))