| 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 tree structure (dict with 'value', 'left', 'right' keys) |
| 15 | path: List of breadcrumbs representing path from root to focus |
| 16 | """ |
| 17 | self.tree = tree |
| 18 | self.path = path |
| 19 | # Current node is determined by following the path from root |
| 20 | self._current = self._get_current_node() |
| 21 | |
| 3 | 22 | @staticmethod |
| 4 | 23 | def from_tree(tree: dict) -> "Zipper": |
| 5 | | pass |
| 6 | | |
| 24 | """ |
| 25 | Create a zipper from a binary tree. |
| 26 | |
| 27 | Args: |
| 28 | tree: A binary tree represented as a dict with 'value', 'left', 'right' keys |
| 29 | |
| 30 | Returns: |
| 31 | A new Zipper instance focused on the root node |
| 32 | """ |
| 33 | # Edge Case: Empty tree |
| 34 | if tree is None: |
| 35 | return None |
| 36 | return Zipper(tree, []) |
| 37 | |
| 38 | def _get_current_node(self): |
| 39 | """ |
| 40 | Get the current focused node by following the path. |
| 41 | |
| 42 | Returns: |
| 43 | The current node dict |
| 44 | """ |
| 45 | current = self.tree |
| 46 | for breadcrumb in self.path: |
| 47 | direction = breadcrumb['direction'] |
| 48 | if direction == 'left': |
| 49 | current = current['left'] |
| 50 | else: # direction == 'right' |
| 51 | current = current['right'] |
| 52 | return current |
| 53 | |
| 7 | 54 | def value(self) -> int: |
| 8 | | pass |
| 9 | | |
| 55 | """ |
| 56 | Get the value of the focus node. |
| 57 | |
| 58 | Returns: |
| 59 | The value of the current node |
| 60 | """ |
| 61 | # Edge Case: Current node is None (should not happen with valid operations) |
| 62 | if self._current is None: |
| 63 | return None |
| 64 | return self._current['value'] |
| 65 | |
| 10 | 66 | def set_value(self, value: int) -> "Zipper": |
| 11 | | pass |
| 12 | | |
| 67 | """ |
| 68 | Set the value of the focus node. |
| 69 | |
| 70 | Args: |
| 71 | value: The new value for the focus node |
| 72 | |
| 73 | Returns: |
| 74 | A new Zipper with the updated value |
| 75 | """ |
| 76 | # Edge Case: Current node is None |
| 77 | if self._current is None: |
| 78 | return self |
| 79 | |
| 80 | # Create a new tree with the updated value |
| 81 | new_tree = self._reconstruct_tree_with_change(None, {'value': value}) |
| 82 | return Zipper(new_tree, self.path) |
| 83 | |
| 13 | 84 | def left(self) -> "Zipper | None": |
| 14 | | pass |
| 15 | | |
| 85 | """ |
| 86 | Move the focus to the left child of the current node. |
| 87 | |
| 88 | Returns: |
| 89 | A new Zipper focused on the left child, or None if no left child exists |
| 90 | """ |
| 91 | # Edge Case: Current node is None |
| 92 | if self._current is None: |
| 93 | return None |
| 94 | |
| 95 | # Edge Case: No left child |
| 96 | if self._current['left'] is None: |
| 97 | return None |
| 98 | |
| 99 | # Create a breadcrumb to remember how to get back to this node |
| 100 | breadcrumb = { |
| 101 | 'parent': self._current, |
| 102 | 'direction': 'left', |
| 103 | 'sibling': self._current['right'] |
| 104 | } |
| 105 | |
| 106 | new_path = self.path + [breadcrumb] |
| 107 | return Zipper(self.tree, new_path) |
| 108 | |
| 16 | 109 | def set_left(self, tree: dict | None) -> "Zipper": |
| 17 | | pass |
| 18 | | |
| 110 | """ |
| 111 | Set the left child of the focus node. |
| 112 | |
| 113 | Args: |
| 114 | tree: The new left subtree (or None to remove left child) |
| 115 | |
| 116 | Returns: |
| 117 | A new Zipper with the updated left child |
| 118 | """ |
| 119 | # Create a new tree with the updated left child |
| 120 | change = {'left': tree} |
| 121 | new_tree = self._reconstruct_tree_with_change('left', change) |
| 122 | return Zipper(new_tree, self.path) |
| 123 | |
| 19 | 124 | def right(self) -> "Zipper | None": |
| 20 | | pass |
| 21 | | |
| 125 | """ |
| 126 | Move the focus to the right child of the current node. |
| 127 | |
| 128 | Returns: |
| 129 | A new Zipper focused on the right child, or None if no right child exists |
| 130 | """ |
| 131 | # Edge Case: Current node is None |
| 132 | if self._current is None: |
| 133 | return None |
| 134 | |
| 135 | # Edge Case: No right child |
| 136 | if self._current['right'] is None: |
| 137 | return None |
| 138 | |
| 139 | # Create a breadcrumb to remember how to get back to this node |
| 140 | breadcrumb = { |
| 141 | 'parent': self._current, |
| 142 | 'direction': 'right', |
| 143 | 'sibling': self._current['left'] |
| 144 | } |
| 145 | |
| 146 | new_path = self.path + [breadcrumb] |
| 147 | return Zipper(self.tree, new_path) |
| 148 | |
| 22 | 149 | def set_right(self, tree: dict | None) -> "Zipper": |
| 23 | | pass |
| 24 | | |
| 150 | """ |
| 151 | Set the right child of the focus node. |
| 152 | |
| 153 | Args: |
| 154 | tree: The new right subtree (or None to remove right child) |
| 155 | |
| 156 | Returns: |
| 157 | A new Zipper with the updated right child |
| 158 | """ |
| 159 | # Create a new tree with the updated right child |
| 160 | change = {'right': tree} |
| 161 | new_tree = self._reconstruct_tree_with_change('right', change) |
| 162 | return Zipper(new_tree, self.path) |
| 163 | |
| 25 | 164 | def up(self) -> "Zipper | None": |
| 26 | | pass |
| 27 | | |
| 165 | """ |
| 166 | Move the focus to the parent of the current node. |
| 167 | |
| 168 | Returns: |
| 169 | A new Zipper focused on the parent, or None if already at root |
| 170 | """ |
| 171 | # Edge Case: Already at root (no path) |
| 172 | if not self.path: |
| 173 | return None |
| 174 | |
| 175 | # Remove the last breadcrumb to move up |
| 176 | new_path = self.path[:-1] |
| 177 | return Zipper(self.tree, new_path) |
| 178 | |
| 28 | 179 | def to_tree(self) -> dict: |
| 29 | | pass |
| 180 | """ |
| 181 | Get the complete tree from the zipper. |
| 182 | |
| 183 | Returns: |
| 184 | The full tree as a dict |
| 185 | """ |
| 186 | return self.tree |
| 187 | |
| 188 | def _reconstruct_tree_with_change(self, direction, change): |
| 189 | """ |
| 190 | Reconstruct the tree with a change at the current focus. |
| 191 | |
| 192 | Args: |
| 193 | direction: The direction of the change ('left', 'right', or None for value) |
| 194 | change: A dict with the change to apply |
| 195 | |
| 196 | Returns: |
| 197 | A new tree with the change applied |
| 198 | """ |
| 199 | # If we're at the root, just apply the change directly |
| 200 | if not self.path: |
| 201 | new_tree = self.tree.copy() |
| 202 | new_tree.update(change) |
| 203 | return new_tree |
| 204 | |
| 205 | # Otherwise, we need to rebuild the tree from the root down |
| 206 | # Start with a copy of the root |
| 207 | new_tree = {'value': self.tree['value'], 'left': self.tree['left'], 'right': self.tree['right']} |
| 208 | |
| 209 | # Follow the path, creating copies of nodes as we go |
| 210 | current_new = new_tree |
| 211 | for i, breadcrumb in enumerate(self.path): |
| 212 | # Create copies of children |
| 213 | if current_new['left'] is not None: |
| 214 | current_new['left'] = { |
| 215 | 'value': current_new['left']['value'], |
| 216 | 'left': current_new['left']['left'], |
| 217 | 'right': current_new['left']['right'] |
| 218 | } |
| 219 | if current_new['right'] is not None: |
| 220 | current_new['right'] = { |
| 221 | 'value': current_new['right']['value'], |
| 222 | 'left': current_new['right']['left'], |
| 223 | 'right': current_new['right']['right'] |
| 224 | } |
| 225 | |
| 226 | # Move to the next node in the path |
| 227 | if breadcrumb['direction'] == 'left': |
| 228 | current_new = current_new['left'] |
| 229 | else: |
| 230 | current_new = current_new['right'] |
| 231 | |
| 232 | # Apply the change to the current node |
| 233 | current_new.update(change) |
| 234 | |
| 235 | return new_tree |
| 236 | |
| 237 | # Handled Edge Cases: Empty tree in from_tree, None current node in value/set_value/left/right, No left/right child in left/right, Already at root in up |