CODEWITHSUNDEEP
python
Nirali
Nirali

Reputation: 1

Adding to a linked list

Can someone please tell me why my add function is not working: (it only adds the first {'a', 3} but not the rest) thankyou

class Frequency(object):
    """
    Stores a letter:frequency pair.

    >>> f = Frequency('c', 2)
    >>> f.letter
    'c'
    >>> f.frequency
    2
    >>> f
    {c: 2}
    """
    def __init__(self, letter, frequency):
        self.letter = letter
        self.frequency = frequency
        self.next = None

    def __repr__(self):
        return '{%s: %d}' % (self.letter, self.frequency)

class SortedFrequencyList(object):
    """
    Stores a collection of Frequency objects as a sorted linked list.
    Items are sorted from the highest frequency to the lowest.
    """
    def __init__(self):
        self.head = None

    def add(self, letter, frequency):
        """
        Adds the given `letter`:`frequency` combination as a Frequency object
        to the list. If the given `letter` is already in the list, the given
        `frequency` is added to its frequency.

        >>> f = SortedFrequencyList()
        >>> f.add('a', 3)
        >>> f
        ({a: 3})
        >>> f.add('b', 2)
        >>> f
        ({a: 3}, {b: 2})
        >>> f.add('c', 4)
        >>> f
        ({c: 4}, {a: 3}, {b: 2})
        >>> f.add('b', 3)
        >>> f
        ({b: 5}, {c: 4}, {a: 3})
        """

        current = self.head
        found = False
        prev = None

        if self.head is None:
            self.head = Frequency(letter, frequency)
        else:
            while current is not None:
                if current.letter == letter:
                    current.frequency = current.frequency + frequency
                    found = True
                prev = current
                current = current.next


            if found is False:
                while current is not None:
                    if current.frequency > frequency:
                        current.next = Frequency(letter, frequency)

                    elif current.frequency < frequency:
                        temp = prev
                        prev = Frequency(letter, frequency)
                        current = temp

                    prev = current
                    current = current.next

Upvotes: 0

Views: 491

Answers (3)

rocksportrocker
rocksportrocker

Reputation: 7419

This is the right time to learn how to use the Python debugger ! You can learn a lot if you use it. Write a testscript which fails and start the debugger with python -m pdb testscript.py. Doug Hellmann writes nice articles about python modules, you should read the one about the pdb module.

Upvotes: 0

Pixou
Pixou

Reputation: 1769

it seems to me that there is another issue. when found is false and current.frequency > frequency, you should set current.next.next to the previous next, something like : temp = current.next current.next=Frequency( current.next.next=temp

Upvotes: 0

6502
6502

Reputation: 114461

The problem is that after the first loop current is always None, therefore the second loop body is never executed even in case found is False.

Upvotes: 2

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