Copying with random pointers in Python

Questions 1 to 5 of 6

1. 1. In the five-node example 7[null] -> 13[7] -> 11[1] -> 10[11] -> 1[7], a single pass copies each node and sets its random pointer in the same step, using copies.get(cur.random). Why does the copy of node 11 end up with random set to None?

   Python raises a TypeError on node 11, so the copy stops thereNode 11 points at itself, so the copy skips itNode 1 has no copy yet when node 11 is processed, so copies.get returns NoneDict keys with the same value are merged, so the lookup returns the wrong copy
2. 2. Which statements about copy_with_map and is_deep_copy are true?

   Pick every answer that is true.

   Node has no __eq__ or __hash__, so a dict compares its keys by identityIf show prints the same text for two lists, the copy is deepThe dict method uses O(1) extra space, because the copy is the same size as the inputis_deep_copy returns False when a copy's random points at an original nodecopy_with_map(None) returns None, because the first loop never runs and mapped(None) returns None
3. 3. Match each term from the lesson to its meaning.

   Choose the matching item for each row.

   Deep copyChoose…placing each copy right after its original, as in `A A' B B'`memory used beyond the input and the outputa copy that reuses the original nodes, so changing the copy changes the originalevery node is a new object, and nothing in the copy points at an original nodeShallow copyChoose…placing each copy right after its original, as in `A A' B B'`memory used beyond the input and the outputa copy that reuses the original nodes, so changing the copy changes the originalevery node is a new object, and nothing in the copy points at an original nodeInterleaveChoose…placing each copy right after its original, as in `A A' B B'`memory used beyond the input and the outputa copy that reuses the original nodes, so changing the copy changes the originalevery node is a new object, and nothing in the copy points at an original nodeExtra spaceChoose…placing each copy right after its original, as in `A A' B B'`memory used beyond the input and the outputa copy that reuses the original nodes, so changing the copy changes the originalevery node is a new object, and nothing in the copy points at an original node
4. 4. Which statements about step 3 of copy_interleaved are true?

   Pick every answer that is true.

   It creates the new Node objects for the copiesIt saves copy.next in next_original before it overwrites copy.nextIf it is skipped, walking from the original head visits six nodes for A -> B -> CIt is the step that sets each copy's random pointerIt gives the last copy a next of None
5. 5. Match each mistake from the Common mistakes section to the symptom it causes.

   Choose the matching item for each row.

   Using copies.get in one pass that also creates the nodesChoose…the copy's random points into the original list, and `is_deep_copy` returns `False`an `AttributeError` when a random pointer is `None`walking from the original head shows six nodes instead of threea forward random pointer is silently lost and becomes `None`Copying copy.random = cur.randomChoose…the copy's random points into the original list, and `is_deep_copy` returns `False`an `AttributeError` when a random pointer is `None`walking from the original head shows six nodes instead of threea forward random pointer is silently lost and becomes `None`Leaving out step 3 of copy_interleavedChoose…the copy's random points into the original list, and `is_deep_copy` returns `False`an `AttributeError` when a random pointer is `None`walking from the original head shows six nodes instead of threea forward random pointer is silently lost and becomes `None`Reading cur.random.next with no None checkChoose…the copy's random points into the original list, and `is_deep_copy` returns `False`an `AttributeError` when a random pointer is `None`walking from the original head shows six nodes instead of threea forward random pointer is silently lost and becomes `None`