2023.08 generic

challenges/2023/08-hauntedWasteland/README.md

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+# [Day 8: Haunted Wasteland](https://adventofcode.com/2023/day/8)

challenges/2023/08-hauntedWasteland/main.py

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+import sys
+import re
+from functools import reduce
+
+
+def parse(instr: str) -> tuple[str, dict[str, tuple[str, str]]]:
+    instructions, raw_graph = instr.split("\n\n")
+    graph = {}
+
+    for (this_node, left, right) in re.findall(r"([A-Z\d]{3}) = \(([A-Z\d]{3}), ([A-Z\d]{3})\)", raw_graph):
+         graph[this_node] = (left, right)
+
+    return instructions, graph
+
+
+def one(instr: str):
+    instructions, graph = parse(instr)
+
+    cursor = "AAA"
+    i = 0
+    while cursor != "ZZZ":
+        instruction = instructions[i % len(instructions)]
+        cursor = graph[cursor][0 if instruction == "L" else 1]
+        i += 1
+
+    return i
+
+
+def are_cursors_at_z(cursors: list[str]) -> bool:
+    for c in cursors:
+        if c[-1] != "Z":
+            return False
+    return True
+
+
+def two(instr: str):
+    instructions, graph = parse(instr)
+
+    cursors = []
+    for key in graph:
+        if key[-1] == "A":
+            cursors.append(key)
+
+    constraints = []
+
+    for start in cursors:
+        cursor = start
+        instruction_step = 0
+        
+        history = {}
+        i = 0
+
+        while (cursor, instruction_step) not in history:
+            instruction = instructions[instruction_step]
+            history[(cursor, instruction_step)] = i
+            cursor = graph[cursor][0 if instruction == "L" else 1]
+            i += 1
+            instruction_step = i % len(instructions)
+        
+        assert reduce(lambda acc, v: acc or v[0][-1] == "Z", history, False), f"{start} has no end condition"
+
+        loop_start_key = (cursor, instruction_step)
+
+        endpoint_at = None
+        for key in history:
+            if key[0][-1] == "Z":
+                endpoint_at = history[key]
+                _debug(key)
+
+        loop_starts_at = history[loop_start_key]
+        loop_length = (max(history.values()) - loop_starts_at) + 1
+
+        _debug(f"{start} loops {loop_start_key} {loop_starts_at=} {endpoint_at=} {loop_length=}")
+
+        constraints.append((loop_starts_at, endpoint_at - loop_starts_at, loop_length))
+
+    m = 0
+    soln = None
+
+    while True:
+        # _debug("---")
+
+        if m % 1000 == 0:
+            _debug(m, end="\r")
+
+        works = True
+
+        for (s, i, l) in constraints:
+            x = (m-s-i)/l
+
+            # _debug((s, i, l), x, (x < 0 or x % 1 != 0))
+
+            if x < 0 or not float(x).is_integer():
+                works = False
+                break
+
+        if works:
+            soln = m
+            break
+
+        m += 1
+
+    return soln
+
+
+def _debug(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print(*args, **kwargs)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2 or sys.argv[1] not in ["1", "2"]:
+        print("Missing day argument", file=sys.stderr)
+        sys.exit(1)
+    inp = sys.stdin.read().strip()
+    if sys.argv[1] == "1":
+        print(one(inp))
+    else:
+        print(two(inp))

challenges/2023/08-hauntedWasteland/tests.json

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+{
+    "1": [
+        {"is": "2", "input": "RL\n\nAAA = (BBB, CCC)\nBBB = (DDD, EEE)\nCCC = (ZZZ, GGG)\nDDD = (DDD, DDD)\nEEE = (EEE, EEE)\nGGG = (GGG, GGG)\nZZZ = (ZZZ, ZZZ)\n"},
+        {"is": "6", "input": "LLR\n\nAAA = (BBB, BBB)\nBBB = (AAA, ZZZ)\nZZZ = (ZZZ, ZZZ)\n"}
+    ],
+    "2": [
+        {"is": "6", "input": "LR\n\n11A = (11B, XXX)\n11B = (XXX, 11Z)\n11Z = (11B, XXX)\n22A = (22B, XXX)\n22B = (22C, 22C)\n22C = (22Z, 22Z)\n22Z = (22B, 22B)\nXXX = (XXX, XXX)\n"}
+    ]
+}