| 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 | The zipper maintains a focus on a specific node in the tree and allows |
| 6 | functional-style navigation and modification operations. |
| 7 | """ |
| 8 | |
| 9 | def __init__(self, tree: dict, path: list = None): |
| 10 | """ |
| 11 | Initialize a Zipper. |
| 12 | |
| 13 | Args: |
| 14 | tree: The binary tree represented as a dict with keys 'value', 'left', 'right' |
| 15 | path: A list of tuples representing the path from root to focus node. |
| 16 | Each tuple contains (parent_node, direction) where direction is 'left' or 'right' |
| 17 | """ |
| 18 | self.tree = tree |
| 19 | self.path = path or [] |
| 20 | |
| 21 | # Navigate to the focus node based on the path |
| 22 | self.focus = self.tree |
| 23 | for parent, direction in self.path: |
| 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, with focus on the root node. |
| 33 | |
| 34 | Args: |
| 35 | tree: A binary tree represented as a dict with keys 'value', 'left', 'right' |
| 36 | |
| 37 | Returns: |
| 38 | A new Zipper instance focused on the root of the tree |
| 39 | |
| 40 | Edge Case: Empty tree (None) - returns a Zipper with None tree and empty focus |
| 41 | """ |
| 42 | # Edge Case: Handle None tree |
| 43 | if tree is None: |
| 44 | return Zipper(None) |
| 45 | |
| 46 | return Zipper(tree) |
| 47 | |
| 7 | 48 | def value(self) -> int: |
| 8 | | pass |
| 9 | | |
| 49 | """ |
| 50 | Get the value of the focus node. |
| 51 | |
| 52 | Returns: |
| 53 | The value of the focus node |
| 54 | |
| 55 | Edge Case: Focus is None - raises AttributeError |
| 56 | """ |
| 57 | # Edge Case: Handle None focus |
| 58 | if self.focus is None: |
| 59 | raise AttributeError("Cannot get value of None focus") |
| 60 | |
| 61 | return self.focus['value'] |
| 62 | |
| 10 | 63 | def set_value(self, value: int) -> "Zipper": |
| 11 | | pass |
| 12 | | |
| 64 | """ |
| 65 | Set the value of the focus node, returning a new zipper. |
| 66 | |
| 67 | Args: |
| 68 | value: The new value for the focus node |
| 69 | |
| 70 | Returns: |
| 71 | A new Zipper with the updated value |
| 72 | |
| 73 | Edge Case: Focus is None - returns a new Zipper with the same state |
| 74 | """ |
| 75 | # Edge Case: Handle None focus |
| 76 | if self.focus is None: |
| 77 | return Zipper(self.tree, self.path) |
| 78 | |
| 79 | # Create a deep copy of the tree |
| 80 | new_tree = self._deep_copy_tree(self.tree) |
| 81 | |
| 82 | # Navigate to the focus node in the new tree |
| 83 | new_focus = new_tree |
| 84 | for parent, direction in self.path: |
| 85 | if direction == 'left': |
| 86 | new_focus = new_focus['left'] |
| 87 | else: # direction == 'right' |
| 88 | new_focus = new_focus['right'] |
| 89 | |
| 90 | # Update the value |
| 91 | new_focus['value'] = value |
| 92 | |
| 93 | return Zipper(new_tree, self.path) |
| 94 | |
| 13 | 95 | def left(self) -> "Zipper | None": |
| 14 | | pass |
| 15 | | |
| 96 | """ |
| 97 | Move the focus to the left child of the current focus node. |
| 98 | |
| 99 | Returns: |
| 100 | A new Zipper focused on the left child, or None if no left child exists |
| 101 | |
| 102 | Edge Case: Focus is None - returns None |
| 103 | Edge Case: No left child - returns None |
| 104 | """ |
| 105 | # Edge Case: Handle None focus |
| 106 | if self.focus is None: |
| 107 | return None |
| 108 | |
| 109 | # Edge Case: No left child |
| 110 | if self.focus['left'] is None: |
| 111 | return None |
| 112 | |
| 113 | # Create a new path that includes the move to the left child |
| 114 | new_path = self.path + [(self.focus, 'left')] |
| 115 | return Zipper(self.tree, new_path) |
| 116 | |
| 16 | 117 | def set_left(self, tree: dict | None) -> "Zipper": |
| 17 | | pass |
| 18 | | |
| 118 | """ |
| 119 | Set the left child of the focus node, returning a new zipper. |
| 120 | |
| 121 | Args: |
| 122 | tree: The new left subtree (or None to remove the left child) |
| 123 | |
| 124 | Returns: |
| 125 | A new Zipper with the updated left child |
| 126 | |
| 127 | Edge Case: Focus is None - returns a new Zipper with the same state |
| 128 | """ |
| 129 | # Edge Case: Handle None focus |
| 130 | if self.focus is None: |
| 131 | return Zipper(self.tree, self.path) |
| 132 | |
| 133 | # Create a deep copy of the tree |
| 134 | new_tree = self._deep_copy_tree(self.tree) |
| 135 | |
| 136 | # Navigate to the focus node in the new tree |
| 137 | new_focus = new_tree |
| 138 | for parent, direction in self.path: |
| 139 | if direction == 'left': |
| 140 | new_focus = new_focus['left'] |
| 141 | else: # direction == 'right' |
| 142 | new_focus = new_focus['right'] |
| 143 | |
| 144 | # Update the left child |
| 145 | new_focus['left'] = tree |
| 146 | |
| 147 | return Zipper(new_tree, self.path) |
| 148 | |
| 19 | 149 | def right(self) -> "Zipper | None": |
| 20 | | pass |
| 21 | | |
| 150 | """ |
| 151 | Move the focus to the right child of the current focus node. |
| 152 | |
| 153 | Returns: |
| 154 | A new Zipper focused on the right child, or None if no right child exists |
| 155 | |
| 156 | Edge Case: Focus is None - returns None |
| 157 | Edge Case: No right child - returns None |
| 158 | """ |
| 159 | # Edge Case: Handle None focus |
| 160 | if self.focus is None: |
| 161 | return None |
| 162 | |
| 163 | # Edge Case: No right child |
| 164 | if self.focus['right'] is None: |
| 165 | return None |
| 166 | |
| 167 | # Create a new path that includes the move to the right child |
| 168 | new_path = self.path + [(self.focus, 'right')] |
| 169 | return Zipper(self.tree, new_path) |
| 170 | |
| 22 | 171 | def set_right(self, tree: dict | None) -> "Zipper": |
| 23 | | pass |
| 24 | | |
| 172 | """ |
| 173 | Set the right child of the focus node, returning a new zipper. |
| 174 | |
| 175 | Args: |
| 176 | tree: The new right subtree (or None to remove the right child) |
| 177 | |
| 178 | Returns: |
| 179 | A new Zipper with the updated right child |
| 180 | |
| 181 | Edge Case: Focus is None - returns a new Zipper with the same state |
| 182 | """ |
| 183 | # Edge Case: Handle None focus |
| 184 | if self.focus is None: |
| 185 | return Zipper(self.tree, self.path) |
| 186 | |
| 187 | # Create a deep copy of the tree |
| 188 | new_tree = self._deep_copy_tree(self.tree) |
| 189 | |
| 190 | # Navigate to the focus node in the new tree |
| 191 | new_focus = new_tree |
| 192 | for parent, direction in self.path: |
| 193 | if direction == 'left': |
| 194 | new_focus = new_focus['left'] |
| 195 | else: # direction == 'right' |
| 196 | new_focus = new_focus['right'] |
| 197 | |
| 198 | # Update the right child |
| 199 | new_focus['right'] = tree |
| 200 | |
| 201 | return Zipper(new_tree, self.path) |
| 202 | |
| 25 | 203 | def up(self) -> "Zipper | None": |
| 26 | | pass |
| 27 | | |
| 204 | """ |
| 205 | Move the focus to the parent of the current focus node. |
| 206 | |
| 207 | Returns: |
| 208 | A new Zipper focused on the parent, or None if focus is at the root |
| 209 | |
| 210 | Edge Case: Focus is at root (empty path) - returns None |
| 211 | Edge Case: Focus is None - returns None |
| 212 | """ |
| 213 | # Edge Case: Handle None focus |
| 214 | if self.focus is None: |
| 215 | return None |
| 216 | |
| 217 | # Edge Case: Already at root |
| 218 | if not self.path: |
| 219 | return None |
| 220 | |
| 221 | # Create a new path that removes the last step (moving up) |
| 222 | new_path = self.path[:-1] |
| 223 | return Zipper(self.tree, new_path) |
| 224 | |
| 28 | 225 | def to_tree(self) -> dict: |
| 29 | | pass |
| 226 | """ |
| 227 | Get the complete tree from the zipper. |
| 228 | |
| 229 | Returns: |
| 230 | The complete binary tree as a dict |
| 231 | |
| 232 | Edge Case: Original tree is None - returns None |
| 233 | """ |
| 234 | # Edge Case: Handle None tree |
| 235 | if self.tree is None: |
| 236 | return None |
| 237 | |
| 238 | return self.tree |
| 239 | |
| 240 | def _deep_copy_tree(self, tree: dict) -> dict: |
| 241 | """ |
| 242 | Create a deep copy of a binary tree. |
| 243 | |
| 244 | Args: |
| 245 | tree: The tree to copy |
| 246 | |
| 247 | Returns: |
| 248 | A deep copy of the tree |
| 249 | """ |
| 250 | if tree is None: |
| 251 | return None |
| 252 | |
| 253 | return { |
| 254 | 'value': tree['value'], |
| 255 | 'left': self._deep_copy_tree(tree['left']), |
| 256 | 'right': self._deep_copy_tree(tree['right']) |
| 257 | } |
| 258 | |
| 259 | # Handled Edge Cases: Empty tree, None focus, No left child, No right child, Focus at root |