| 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 maintains a focus on a specific node in the tree and allows |
| 6 | functional navigation and modification operations. |
| 7 | """ |
| 8 | |
| 9 | def __init__(self, tree, path): |
| 10 | """ |
| 11 | Initialize a Zipper. |
| 12 | |
| 13 | Args: |
| 14 | tree: The full tree structure (dict with 'value', 'left', 'right' keys) |
| 15 | path: A list of breadcrumbs representing the path from root to focus |
| 16 | """ |
| 17 | self.tree = tree |
| 18 | self.path = path |
| 19 | |
| 20 | # Calculate the current focus based on the path |
| 21 | self.focus = tree |
| 22 | for breadcrumb in self.path: |
| 23 | direction = breadcrumb['direction'] |
| 24 | if direction == 'left': |
| 25 | self.focus = self.focus['left'] |
| 26 | else: # direction == 'right' |
| 27 | self.focus = self.focus['right'] |
| 28 | |
| 3 | 29 | @staticmethod |
| 4 | 30 | def from_tree(tree: dict) -> "Zipper": |
| 5 | | pass |
| 6 | | |
| 31 | """ |
| 32 | Create a zipper from a binary tree. |
| 33 | |
| 34 | Args: |
| 35 | tree: A binary tree represented as a dict with 'value', 'left', 'right' keys |
| 36 | |
| 37 | Returns: |
| 38 | A new Zipper instance focused on the root of the tree |
| 39 | """ |
| 40 | # Edge Case: Handle None tree input |
| 41 | if tree is None: |
| 42 | return None |
| 43 | |
| 44 | return Zipper(tree, []) |
| 45 | |
| 7 | 46 | def value(self) -> int: |
| 8 | | pass |
| 9 | | |
| 47 | """ |
| 48 | Get the value of the focus node. |
| 49 | |
| 50 | Returns: |
| 51 | The value of the focus node |
| 52 | """ |
| 53 | # Edge Case: Handle None focus |
| 54 | if self.focus is None: |
| 55 | return None |
| 56 | |
| 57 | return self.focus['value'] |
| 58 | |
| 10 | 59 | def set_value(self, value: int) -> "Zipper": |
| 11 | | pass |
| 12 | | |
| 60 | """ |
| 61 | Set the value of the focus node. |
| 62 | |
| 63 | Args: |
| 64 | value: The new value for the focus node |
| 65 | |
| 66 | Returns: |
| 67 | A new Zipper with the updated value |
| 68 | """ |
| 69 | # Edge Case: Handle None focus |
| 70 | if self.focus is None: |
| 71 | return self |
| 72 | |
| 73 | # Create a new tree with the updated value |
| 74 | new_tree = self._rebuild_tree_with_focus_change({'value': value, 'left': self.focus['left'], 'right': self.focus['right']}) |
| 75 | return Zipper(new_tree, self.path) |
| 76 | |
| 13 | 77 | def left(self) -> "Zipper | None": |
| 14 | | pass |
| 15 | | |
| 78 | """ |
| 79 | Move the focus to the left child of the current node. |
| 80 | |
| 81 | Returns: |
| 82 | A new Zipper focused on the left child, or None if no left child exists |
| 83 | """ |
| 84 | # Edge Case: Handle None focus |
| 85 | if self.focus is None or self.focus['left'] is None: |
| 86 | return None |
| 87 | |
| 88 | # Create a breadcrumb to remember how we got to the current focus |
| 89 | breadcrumb = { |
| 90 | 'parent': self.focus, |
| 91 | 'direction': 'left', |
| 92 | 'sibling': self.focus['right'] |
| 93 | } |
| 94 | |
| 95 | new_path = self.path + [breadcrumb] |
| 96 | return Zipper(self.tree, new_path) |
| 97 | |
| 16 | 98 | def set_left(self, tree: dict | None) -> "Zipper": |
| 17 | | pass |
| 18 | | |
| 99 | """ |
| 100 | Set the left child of the focus node. |
| 101 | |
| 102 | Args: |
| 103 | tree: The new left subtree (or None to remove the left child) |
| 104 | |
| 105 | Returns: |
| 106 | A new Zipper with the updated left child |
| 107 | """ |
| 108 | # Edge Case: Handle None focus |
| 109 | if self.focus is None: |
| 110 | return self |
| 111 | |
| 112 | # Create a new focus node with the updated left child |
| 113 | new_focus = { |
| 114 | 'value': self.focus['value'], |
| 115 | 'left': tree, |
| 116 | 'right': self.focus['right'] |
| 117 | } |
| 118 | |
| 119 | new_tree = self._rebuild_tree_with_focus_change(new_focus) |
| 120 | return Zipper(new_tree, self.path) |
| 121 | |
| 19 | 122 | def right(self) -> "Zipper | None": |
| 20 | | pass |
| 21 | | |
| 123 | """ |
| 124 | Move the focus to the right child of the current node. |
| 125 | |
| 126 | Returns: |
| 127 | A new Zipper focused on the right child, or None if no right child exists |
| 128 | """ |
| 129 | # Edge Case: Handle None focus |
| 130 | if self.focus is None or self.focus['right'] is None: |
| 131 | return None |
| 132 | |
| 133 | # Create a breadcrumb to remember how we got to the current focus |
| 134 | breadcrumb = { |
| 135 | 'parent': self.focus, |
| 136 | 'direction': 'right', |
| 137 | 'sibling': self.focus['left'] |
| 138 | } |
| 139 | |
| 140 | new_path = self.path + [breadcrumb] |
| 141 | return Zipper(self.tree, new_path) |
| 142 | |
| 22 | 143 | def set_right(self, tree: dict | None) -> "Zipper": |
| 23 | | pass |
| 24 | | |
| 144 | """ |
| 145 | Set the right child of the focus node. |
| 146 | |
| 147 | Args: |
| 148 | tree: The new right subtree (or None to remove the right child) |
| 149 | |
| 150 | Returns: |
| 151 | A new Zipper with the updated right child |
| 152 | """ |
| 153 | # Edge Case: Handle None focus |
| 154 | if self.focus is None: |
| 155 | return self |
| 156 | |
| 157 | # Create a new focus node with the updated right child |
| 158 | new_focus = { |
| 159 | 'value': self.focus['value'], |
| 160 | 'left': self.focus['left'], |
| 161 | 'right': tree |
| 162 | } |
| 163 | |
| 164 | new_tree = self._rebuild_tree_with_focus_change(new_focus) |
| 165 | return Zipper(new_tree, self.path) |
| 166 | |
| 25 | 167 | def up(self) -> "Zipper | None": |
| 26 | | pass |
| 27 | | |
| 168 | """ |
| 169 | Move the focus to the parent of the current node. |
| 170 | |
| 171 | Returns: |
| 172 | A new Zipper focused on the parent node, or None if already at root |
| 173 | """ |
| 174 | # Edge Case: Handle when already at root (no path) |
| 175 | if not self.path: |
| 176 | return None |
| 177 | |
| 178 | # Remove the last breadcrumb to move up |
| 179 | new_path = self.path[:-1] |
| 180 | return Zipper(self.tree, new_path) |
| 181 | |
| 28 | 182 | def to_tree(self) -> dict: |
| 29 | | pass |
| 183 | """ |
| 184 | Get the full tree from the zipper. |
| 185 | |
| 186 | Returns: |
| 187 | The full binary tree |
| 188 | """ |
| 189 | return self.tree |
| 190 | |
| 191 | def _rebuild_tree_with_focus_change(self, new_focus): |
| 192 | """ |
| 193 | Rebuild the tree with a modified focus node. |
| 194 | |
| 195 | Args: |
| 196 | new_focus: The new focus node |
| 197 | |
| 198 | Returns: |
| 199 | A new tree with the focus node updated |
| 200 | """ |
| 201 | # If we're at the root, just return the new focus as the tree |
| 202 | if not self.path: |
| 203 | return new_focus |
| 204 | |
| 205 | # Rebuild the tree from the bottom up using the path |
| 206 | rebuilt_node = new_focus |
| 207 | |
| 208 | # Process breadcrumbs in reverse order (from focus up to root) |
| 209 | for breadcrumb in reversed(self.path): |
| 210 | parent = breadcrumb['parent'] |
| 211 | direction = breadcrumb['direction'] |
| 212 | sibling = breadcrumb['sibling'] |
| 213 | |
| 214 | if direction == 'left': |
| 215 | rebuilt_node = { |
| 216 | 'value': parent['value'], |
| 217 | 'left': rebuilt_node, |
| 218 | 'right': sibling |
| 219 | } |
| 220 | else: # direction == 'right' |
| 221 | rebuilt_node = { |
| 222 | 'value': parent['value'], |
| 223 | 'left': sibling, |
| 224 | 'right': rebuilt_node |
| 225 | } |
| 226 | |
| 227 | return rebuilt_node |
| 228 | |
| 229 | # Handled Edge Cases: None tree input, None focus, moving to non-existent child, already at root |