2021: d18: ex2: add solution
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2021/d18/ex2/ex2.py
Executable file
210
2021/d18/ex2/ex2.py
Executable file
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#!/usr/bin/env python
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import itertools
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import sys
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from copy import deepcopy
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from dataclasses import dataclass
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from typing import Iterator, List, Optional, Tuple
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@dataclass
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class Tree:
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parent: Optional["Pair"]
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@dataclass
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class Pair(Tree):
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left: Tree
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right: Tree
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@dataclass
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class Num(Tree):
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val: int
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# True means left, False means right
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Path = List[bool]
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def solve(input: List[str]) -> int:
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def make_pair(left: Tree, right: Tree, parent: Optional[Pair] = None) -> Pair:
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pair = Pair(parent=parent, left=left, right=right)
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pair.left.parent = pair
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pair.right.parent = pair
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return pair
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def make_num(val: int, parent: Optional[Pair] = None) -> Num:
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return Num(parent=parent, val=val)
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# FIXME: remove this
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def debug(tree: Tree) -> str:
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if isinstance(tree, Pair):
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return f"[{debug(tree.left)},{debug(tree.right)}]"
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assert isinstance(tree, Num)
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return str(tree.val)
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def parse() -> List[Tree]:
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def parse_snailfish_number(line: str) -> Tree:
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def parse_index(input: str, index: int = 0) -> Tuple[int, Tree]:
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if input[index] == "[":
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left_index, left = parse_index(input, index + 1)
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assert input[left_index] == "," # Sanity check
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right_index, right = parse_index(input, left_index + 1)
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assert input[right_index] == "]" # Sanity check
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return right_index + 1, make_pair(left, right)
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res = 0
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for i in itertools.count(index):
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if i < len(input) and input[i] in set(str(i) for i in range(10)):
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res = res * 10 + int(input[i])
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else:
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return i, make_num(res)
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assert False # Sanity check
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__, res = parse_index(line)
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return res
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return [parse_snailfish_number(line) for line in input]
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def explosion_path(number: Tree) -> Optional[Path]:
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def dfs(number: Pair, path: Path = []) -> Optional[Path]:
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if (
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len(path) >= 4
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and isinstance(number.left, Num)
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and isinstance(number.right, Num)
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):
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return path
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if isinstance(number.left, Pair):
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left_path = dfs(number.left, path + [True])
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if left_path is not None:
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return left_path
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if isinstance(number.right, Pair):
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right_path = dfs(number.right, path + [False])
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if right_path is not None:
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return right_path
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return None
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assert isinstance(number, Pair) # Sanity check
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return dfs(number)
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def split_path(number: Tree) -> Optional[Path]:
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def dfs(number: Pair, path: Path = []) -> Optional[Path]:
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if isinstance(number.left, Num):
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if number.left.val >= 10:
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return path + [True]
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else:
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assert isinstance(number.left, Pair) # Sanity check
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if (left_path := dfs(number.left, path + [True])) is not None:
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return left_path
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if isinstance(number.right, Num):
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if number.right.val >= 10:
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return path + [False]
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else:
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assert isinstance(number.right, Pair) # Sanity check
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if (right_path := dfs(number.right, path + [False])) is not None:
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return right_path
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return None
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assert isinstance(number, Pair) # Sanity check
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return dfs(number)
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def explode(number: Tree, path: Path) -> Tree:
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def walk(number: Tree, reverse: bool) -> Iterator[Tree]:
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if isinstance(number, Num):
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yield number
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else:
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assert isinstance(number, Pair) # Sanity check
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first, second = (
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(number.right, number.left)
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if reverse
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else (number.left, number.right)
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)
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yield from walk(first, reverse)
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yield number
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yield from walk(second, reverse)
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def next_num(number: Tree, reverse: bool) -> Optional[Num]:
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if number.parent is None:
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return None
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sibling = number.parent.left if reverse else number.parent.right
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if number is sibling:
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return next_num(number.parent, reverse)
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for node in walk(sibling, reverse=reverse):
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if isinstance(node, Num):
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return node
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return None
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assert isinstance(number, Pair) # Sanity check
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if len(path) == 0:
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p, n = next_num(number, reverse=True), next_num(number, reverse=False)
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if p is not None:
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assert isinstance(number.left, Num) # Safety check
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p.val += number.left.val
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if n is not None:
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assert isinstance(number.right, Num) # Safety check
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n.val += number.right.val
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return make_num(0)
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parent, left, right = number.parent, number.left, number.right
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if path[0]:
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left = explode(number.left, path[1:])
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else:
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right = explode(number.right, path[1:])
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return make_pair(parent=parent, left=left, right=right)
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def split(number: Tree, path: Path) -> Tree:
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def split_int(num: int, parent: Optional[Pair]) -> Tree:
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assert num >= 0 # Sanity check
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left = num // 2
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right = num - left
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res = make_pair(left=make_num(left), right=make_num(right), parent=parent)
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return res
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if len(path) == 0:
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assert isinstance(number, Num) # Sanity check
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return split_int(number.val, number.parent)
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assert isinstance(number, Pair) # Sanity check
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parent, left, right = number.parent, number.left, number.right
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if path[0]:
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left = split(number.left, path[1:])
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else:
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right = split(number.right, path[1:])
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return make_pair(parent=parent, left=left, right=right)
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def reduce(number: Tree) -> Tree:
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path = explosion_path(number)
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if path is not None:
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return reduce(explode(number, path))
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path = split_path(number)
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if path is not None:
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return reduce(split(number, path))
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return number
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def add(left: Tree, right: Tree) -> Tree:
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return reduce(make_pair(left=left, right=right))
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def magnitude(number: Tree) -> int:
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if isinstance(number, Num):
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return number.val
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assert isinstance(number, Pair) # Safety check
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return 3 * magnitude(number.left) + 2 * magnitude(number.right)
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numbers = parse()
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return max(
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magnitude(add(deepcopy(l), deepcopy(r)))
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for l, r in itertools.permutations(numbers, 2)
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)
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def main() -> None:
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input = [line.strip() for line in sys.stdin.readlines()]
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print(solve(input))
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if __name__ == "__main__":
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main()
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