Created
April 8, 2023 21:54
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Python example of a tree that uses arena allocation
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| from typing import TypeVar, List, Optional | |
| from functools import partial | |
| T = TypeVar('T') | |
| class TreeNodeTy: | |
| pass | |
| class TreeNode(TreeNodeTy): | |
| def __init__( | |
| self, | |
| value: T, | |
| idx: int, | |
| arena: List[TreeNodeTy], | |
| left: Optional[int] = None, | |
| right: Optional[int] = None, | |
| ): | |
| self.arena_ref = arena | |
| self.value = value | |
| self.idx = idx | |
| self.left, self.right = left, right | |
| class Tree: | |
| def __init__(self): | |
| self.arena: List[TreeNode] = [] | |
| @property | |
| def size(self) -> int: | |
| return len(self.arena) | |
| def __append(self, elem: TreeNode): | |
| self.arena.append(elem) | |
| return self.size - 1 | |
| def is_empty(self): | |
| return not self.size | |
| @classmethod | |
| def from_list(cls, items: List[T]): | |
| tree = cls() | |
| for item in items: | |
| tree.insert(item) | |
| return tree | |
| def to_list(self, traversal_type='inorder'): | |
| traversal = [] | |
| def add_elem(elem: TreeNode): | |
| traversal.append(elem.value) | |
| def go(side, elem: TreeNode): | |
| if child_index := getattr(elem, side): | |
| traverse(child_index) | |
| go_left = partial(go, 'left') | |
| go_right = partial(go, 'right') | |
| actions = { | |
| 'inorder': [go_left, add_elem, go_right], | |
| 'preorder': [add_elem, go_left, go_right], | |
| 'postorder': [go_left, go_right, add_elem] | |
| } | |
| def traverse(k=0): | |
| curr = self.arena[k] | |
| for action in actions[traversal_type]: | |
| action(curr) | |
| traverse(0) | |
| return traversal | |
| def insert(self, value): | |
| new_node = TreeNode( | |
| value=value, | |
| arena=self.arena, | |
| idx=self.size | |
| ) | |
| if self.is_empty(): | |
| self.__append(new_node) | |
| else: | |
| curr_idx = 0 | |
| while True: | |
| curr_node = self.arena[curr_idx] | |
| curr_val = curr_node.value | |
| left_idx = curr_node.left | |
| right_idx = curr_node.right | |
| if value > curr_val: | |
| if right_idx is None: | |
| curr_node.right = self.__append(new_node) | |
| break | |
| curr_idx = right_idx | |
| else: | |
| if left_idx is None: | |
| curr_node.left = self.__append(new_node) | |
| break | |
| curr_idx = left_idx | |
| xs = [10, 3, 9, 7, 1, 4, 5, 2, 6] | |
| arena_tree = Tree.from_list(xs) | |
| inorder_elems = arena_tree.to_list() | |
| print(inorder_elems) |
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