Palindrome and partition in Python

Questions 1 to 5 of 7

1. 1. Put the four steps of the palindrome check in the order the lesson runs them.

   Use the arrows to put the steps in order.

   1. 1.Compare the first half with the reversed second half, pair by pair↑↓
   2. 2.Reverse the second half again to restore the list↑↓
   3. 3.Reverse the second half, starting at the slow pointer↑↓
   4. 4.Find the middle with a slow pointer and a fast pointer↑↓
2. 2. Why must the restore step (reversing the second half again) run even when the comparison has already found a mismatch?

   Otherwise Python raises an AttributeError on the next callOtherwise the caller's list is left with its second half reversed, so the list is damagedOtherwise the garbage collector cannot free the slow pointerBecause the answer is only final after the restore has run
3. 3. Using is_palindrome, build and show from the palindrome lesson, what does this code print? ``python h = build([4, 5, 4, 5]) print(is_palindrome(h), show(h)) ``

   True 4 -> 5 -> 4 -> 5 -> nullFalse 4 -> 5 -> 5 -> 4 -> nullFalse 5 -> 4 -> 5 -> 4 -> nullFalse 4 -> 5 -> 4 -> 5 -> null
4. 4. In split, the line nxt = cur.next comes before yes.add(cur). Why does it have to come first?

   add sets the node's next to None, so reading cur.next after the add would end the walk after one nodePython needs a copy of every node before it can add it to a chainIt stops the dummy node from being garbage-collectedIt makes the last node of the chain point back at the head of the original list
5. 5. Using partition from this lesson, with build and show from the palindrome lesson, what does this code print? ``python h = build([3, 1, 4, 1, 5]) print(show(partition(h, 4))) ``

   3 -> 1 -> 4 -> 1 -> 5 -> null1 -> 1 -> 3 -> 4 -> 5 -> null3 -> 1 -> 1 -> 4 -> 5 -> null4 -> 5 -> 3 -> 1 -> 1 -> null