Question

The following SinglyLinkedList class is available:

class SinglyLinkedList:
    class _Node:
        """Lightweight, nonpublic class for storing a singly linked node."""
        __slots__ = 'element', 'next'       # streamline memory usage

        def __init__(self, element, next):  # initialize node's fields
            self.element = element          # reference to user's element
            self.next = next                # reference to next node

    def __init__(self):          # initialize list's fields
        self._head = None        # head references to None

    def printList(self, label):
        print(label, end=' ')
        curr = self._head
        while curr != None:
            print(curr.element, end=" -> ")
            curr = curr.next
        print("/")

    #########################################################
    # Only this method is required for your solution
    def computeStats(self):
        # Your code goes here

    #########################################################

def main():
    # Create a list object for testing purpose
    sList = SinglyLinkedList()

    # Create list 2 -> 4 -> -1 -> 8 -> -5
    sList._head = sList._Node(2, sList._Node(4, sList._Node(-1, sList._Node(8, sList._Node(-5, None)))))
    sList.printList("before:")

    # Call computeStats method
    sList.computeStats()

    # And see if it worked!
    sList.printList("after :")

if __name__=="__main__":
    main()

Assume you have a singly-linked list of integers, some positive and some negative. Write a Python method that traverses this list to calculate both the average and the count (ie, number) of the odd values only. Once calculated, add the average to a new node at the front of the list, and the count to a new node at the end of the list. You may assume that the list will always contain at least one odd value.

Your method will be have the following method signature:

def computeStats(self):

You may use only the SinglyLinkedList class; no other methods (like size(), etc) are available.

For example, if the list initially contains:

2 → 4 → -1 → 8 → -5

the resulting list will contain:

-3.0 → 2 → 4 → -1 → 8 → -5 → 2

Answer 1

class SinglyLinkedList:
    class _Node:
        """Lightweight, nonpublic class for storing a singly linked node."""
        __slots__ = 'element', 'next'       # streamline memory usage

        def __init__(self, element, next):  # initialize node's fields
            self.element = element          # reference to user's element
            self.next = next                # reference to next node

    def __init__(self):          # initialize list's fields
        self._head = None        # head references to None

    def printList(self, label):
        print(label, end=' ')
        curr = self._head
        while curr != None:
            print(curr.element, end=" -> ")
            curr = curr.next
        print("/")

    #########################################################
    # Only this method is required for your solution
    def computeStats(self):
        # Your code goes here
        sum = 0
        count = 0
        curr = self._head
        pre = None
        while curr != None:
            if curr.element % 2 == 1:
                count += 1
                sum += curr.element
            pre = curr
            curr = curr.next
        pre.next = self._Node(count, None)
        newnode = self._Node(sum/count, self._head)
        self._head = newnode
    #########################################################

def main():
    # Create a list object for testing purpose
    sList = SinglyLinkedList()

    # Create list 2 -> 4 -> -1 -> 8 -> -5
    sList._head = sList._Node(2, sList._Node(4, sList._Node(-1, sList._Node(8, sList._Node(-5, None)))))
    sList.printList("before:")

    # Call computeStats method
    sList.computeStats()

    # And see if it worked!
    sList.printList("after :")

if __name__=="__main__":
    main()


Output

before: 2 -> 4 -> -1 -> 8 -> -5 -> /
after : -3.0 -> 2 -> 4 -> -1 -> 8 -> -5 -> 2 -> /

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