| 1 | 1 | class Zipper: |
| 2 | | # Tree is a dict with keys "value" (int), "left" (dict or None), "right" (dict or None) |
| 2 | """ |
| 3 | A zipper for navigating and manipulating a binary tree. |
| 4 | |
| 5 | A zipper contains a data structure and a pointer (focus) into that structure. |
| 6 | It supports moving through the tree and modifying it in a functional way. |
| 7 | """ |
| 8 | |
| 9 | def __init__(self, tree, breadcrumbs=None): |
| 10 | """ |
| 11 | Initialize a Zipper. |
| 12 | |
| 13 | Args: |
| 14 | tree: The current subtree (focus) as a dict with keys 'value', 'left', 'right' |
| 15 | breadcrumbs: A list of tuples tracking the path back to the root |
| 16 | """ |
| 17 | self.tree = tree |
| 18 | self.breadcrumbs = breadcrumbs or [] |
| 19 | |
| 3 | 20 | @staticmethod |
| 4 | 21 | def from_tree(tree: dict) -> "Zipper": |
| 5 | | pass |
| 6 | | |
| 22 | """ |
| 23 | Create a zipper from a binary tree. |
| 24 | |
| 25 | Args: |
| 26 | tree: A binary tree represented as a dict with keys 'value', 'left', 'right' |
| 27 | |
| 28 | Returns: |
| 29 | A new Zipper instance focused on the root of the tree |
| 30 | |
| 31 | Edge Case: Empty tree (None) is handled by creating an empty zipper |
| 32 | """ |
| 33 | # Edge Case: Handle None tree |
| 34 | if tree is None: |
| 35 | return Zipper(None) |
| 36 | return Zipper(tree) |
| 37 | |
| 7 | 38 | def value(self) -> int: |
| 8 | | pass |
| 9 | | |
| 39 | """ |
| 40 | Get the value of the focus node. |
| 41 | |
| 42 | Returns: |
| 43 | The value of the current node |
| 44 | |
| 45 | Edge Case: If the current tree is None, this would raise an error in a real implementation, |
| 46 | but based on the problem constraints, we assume the tree is valid when this method is called. |
| 47 | """ |
| 48 | return self.tree["value"] |
| 49 | |
| 10 | 50 | def set_value(self, value: int) -> "Zipper": |
| 11 | | pass |
| 12 | | |
| 51 | """ |
| 52 | Set the value of the focus node. |
| 53 | |
| 54 | Args: |
| 55 | value: The new value for the focus node |
| 56 | |
| 57 | Returns: |
| 58 | A new Zipper with the updated value |
| 59 | |
| 60 | Edge Case: If the current tree is None, creates a new node with the given value |
| 61 | """ |
| 62 | # Edge Case: If current tree is None, create a new node |
| 63 | if self.tree is None: |
| 64 | new_tree = {"value": value, "left": None, "right": None} |
| 65 | else: |
| 66 | new_tree = {"value": value, "left": self.tree["left"], "right": self.tree["right"]} |
| 67 | return Zipper(new_tree, self.breadcrumbs) |
| 68 | |
| 13 | 69 | def left(self) -> "Zipper | None": |
| 14 | | pass |
| 15 | | |
| 70 | """ |
| 71 | Move the focus to the left child of the current node. |
| 72 | |
| 73 | Returns: |
| 74 | A new Zipper focused on the left child, or None if there is no left child |
| 75 | |
| 76 | Edge Case: If there's no left child or current tree is None, returns None |
| 77 | """ |
| 78 | # Edge Case: Current tree is None |
| 79 | if self.tree is None: |
| 80 | return None |
| 81 | |
| 82 | # Edge Case: No left child |
| 83 | if self.tree["left"] is None: |
| 84 | return None |
| 85 | |
| 86 | # Create breadcrumb to remember how to reconstruct the parent |
| 87 | breadcrumb = { |
| 88 | "parent": { |
| 89 | "value": self.tree["value"], |
| 90 | "right": self.tree["right"] |
| 91 | }, |
| 92 | "is_left": True |
| 93 | } |
| 94 | |
| 95 | return Zipper(self.tree["left"], self.breadcrumbs + [breadcrumb]) |
| 96 | |
| 16 | 97 | def set_left(self, tree: dict | None) -> "Zipper": |
| 17 | | pass |
| 18 | | |
| 98 | """ |
| 99 | Set the left child of the focus node. |
| 100 | |
| 101 | Args: |
| 102 | tree: The new left subtree (or None to remove the left child) |
| 103 | |
| 104 | Returns: |
| 105 | A new Zipper with the updated left child |
| 106 | |
| 107 | Edge Case: If current tree is None, creates a new node with the given left subtree |
| 108 | """ |
| 109 | # Edge Case: If current tree is None, create a new node |
| 110 | if self.tree is None: |
| 111 | new_tree = {"value": 0, "left": tree, "right": None} # Default value 0 |
| 112 | else: |
| 113 | new_tree = {"value": self.tree["value"], "left": tree, "right": self.tree["right"]} |
| 114 | return Zipper(new_tree, self.breadcrumbs) |
| 115 | |
| 19 | 116 | def right(self) -> "Zipper | None": |
| 20 | | pass |
| 21 | | |
| 117 | """ |
| 118 | Move the focus to the right child of the current node. |
| 119 | |
| 120 | Returns: |
| 121 | A new Zipper focused on the right child, or None if there is no right child |
| 122 | |
| 123 | Edge Case: If there's no right child or current tree is None, returns None |
| 124 | """ |
| 125 | # Edge Case: Current tree is None |
| 126 | if self.tree is None: |
| 127 | return None |
| 128 | |
| 129 | # Edge Case: No right child |
| 130 | if self.tree["right"] is None: |
| 131 | return None |
| 132 | |
| 133 | # Create breadcrumb to remember how to reconstruct the parent |
| 134 | breadcrumb = { |
| 135 | "parent": { |
| 136 | "value": self.tree["value"], |
| 137 | "left": self.tree["left"] |
| 138 | }, |
| 139 | "is_left": False |
| 140 | } |
| 141 | |
| 142 | return Zipper(self.tree["right"], self.breadcrumbs + [breadcrumb]) |
| 143 | |
| 22 | 144 | def set_right(self, tree: dict | None) -> "Zipper": |
| 23 | | pass |
| 24 | | |
| 145 | """ |
| 146 | Set the right child of the focus node. |
| 147 | |
| 148 | Args: |
| 149 | tree: The new right subtree (or None to remove the right child) |
| 150 | |
| 151 | Returns: |
| 152 | A new Zipper with the updated right child |
| 153 | |
| 154 | Edge Case: If current tree is None, creates a new node with the given right subtree |
| 155 | """ |
| 156 | # Edge Case: If current tree is None, create a new node |
| 157 | if self.tree is None: |
| 158 | new_tree = {"value": 0, "left": None, "right": tree} # Default value 0 |
| 159 | else: |
| 160 | new_tree = {"value": self.tree["value"], "left": self.tree["left"], "right": tree} |
| 161 | return Zipper(new_tree, self.breadcrumbs) |
| 162 | |
| 25 | 163 | def up(self) -> "Zipper | None": |
| 26 | | pass |
| 27 | | |
| 164 | """ |
| 165 | Move the focus to the parent of the current node. |
| 166 | |
| 167 | Returns: |
| 168 | A new Zipper focused on the parent, or None if there is no parent (at root) |
| 169 | |
| 170 | Edge Case: If there are no breadcrumbs (at root), returns None |
| 171 | """ |
| 172 | # Edge Case: Already at root (no breadcrumbs) |
| 173 | if not self.breadcrumbs: |
| 174 | return None |
| 175 | |
| 176 | # Get the last breadcrumb |
| 177 | last_breadcrumb = self.breadcrumbs[-1] |
| 178 | parent_info = last_breadcrumb["parent"] |
| 179 | is_left = last_breadcrumb["is_left"] |
| 180 | |
| 181 | # Reconstruct the parent tree |
| 182 | if is_left: |
| 183 | # We were the left child |
| 184 | reconstructed_tree = { |
| 185 | "value": parent_info["value"], |
| 186 | "left": self.tree, |
| 187 | "right": parent_info["right"] |
| 188 | } |
| 189 | else: |
| 190 | # We were the right child |
| 191 | reconstructed_tree = { |
| 192 | "value": parent_info["value"], |
| 193 | "left": parent_info["left"], |
| 194 | "right": self.tree |
| 195 | } |
| 196 | |
| 197 | return Zipper(reconstructed_tree, self.breadcrumbs[:-1]) |
| 198 | |
| 28 | 199 | def to_tree(self) -> dict: |
| 29 | | pass |
| 200 | """ |
| 201 | Get the complete binary tree from the zipper. |
| 202 | |
| 203 | Returns: |
| 204 | The complete binary tree as a dict |
| 205 | |
| 206 | Edge Case: If the current focus is None, reconstructs the tree from breadcrumbs |
| 207 | """ |
| 208 | # Start with the current tree |
| 209 | current = self.tree |
| 210 | |
| 211 | # Work backwards through breadcrumbs to reconstruct the full tree |
| 212 | for breadcrumb in reversed(self.breadcrumbs): |
| 213 | parent_info = breadcrumb["parent"] |
| 214 | is_left = breadcrumb["is_left"] |
| 215 | |
| 216 | if is_left: |
| 217 | # Current was the left child |
| 218 | current = { |
| 219 | "value": parent_info["value"], |
| 220 | "left": current, |
| 221 | "right": parent_info["right"] |
| 222 | } |
| 223 | else: |
| 224 | # Current was the right child |
| 225 | current = { |
| 226 | "value": parent_info["value"], |
| 227 | "left": parent_info["left"], |
| 228 | "right": current |
| 229 | } |
| 230 | |
| 231 | return current |
| 232 | |
| 233 | # Handled Edge Cases: Empty tree, None tree, no children, no parent, setting values on None nodes |