Unable to Insert node in Circular Singly linked list-CodePudding

I'm not able to get the desired output in the given code. The code is about inserting nodes in the circular singly linked list. Please correct this code as per the problems stated.

class Node:
    def __init__(self,value):
        self.value = value
        self.next = None
 
class CircularSLL:
    
    def __init__(self):
        self.head = None
        self.tail = None
        
    def __iter__(self):
        node = self.head
        while node:
            yield node
            if node.next == self.head:
                print('break')
                break
            node = node.next
            
    def insertnode(self, value, location):
        new_node = Node(value)
        
        # check if head is None or not
        
        if self.head is None:
            self.head = new_node
            self.tail = new_node
            new_node.next = self.head
            
        else:
            
            
            
            # At the start
            if location == 0:
                new_node.next = self.head
                self.head = new_node
                self.tail.next = self.head
            
            # At the end
            elif location == -1:
                new_node.next = self.tail.next
                self.tail.next = new_node
                self.tail = new_node
                
            else:
                
                # At specific location
                temp_node = self.head
                index = 0
                
                while index < location - 1:
                    
                    # node is the last element
                    if temp_node.next == self.head:
                        break
                    temp_node = temp_node.next
                    index  = 1
                
                next_node = temp_node.next
                temp_node.next = new_node
                new_node.next = next_node
                
                if temp_node.next == self.head:
                    self.tail == temp_node
                    self.tail.next = self.head
                
            return 'The node has been successfully inserted'
 
cll = CircularSLL()
 
cll.insertnode(1,0)
 
cll.insertnode(3, 1)
 
cll.insertnode(4, 2)
 
cll.insertnode(5, 3)
 
cll.insertnode(6, 4)
 
print([node.value for node in call])

output = [1,3,4,5,6 ]

1st problem - when inserting at index = '0'.

cll.insertnode(10,0)

output = [10,1]

expected

output = [10,1,3,4,5,6]

2nd problem - when putting location = '-1'

cll.insertnode(30, -1)

output = [1, 30]

expected

output = [10,1,3,4,5,6,30]

CodePudding user response：

With your test setup, tail is never getting set after the first node is inserted.

(Pdb) [c.value for c in cll]
[1, 3, 4, 5, 6]
(Pdb) cll.head.value
1
(Pdb) cll.tail.value
1
(Pdb) cll.head is cll.tail
True

Your first problem is you have self.tail == temp_node instead of self.tail = temp_node, so let's fix that. Still, we're not getting the expected output:

[1, 3, 4, 5, 6]

The next problem is that by the time you check if temp_node.next is self.head:, you have already set temp_node.next to be new_node. It will never be self.head. I believe you intended to check new_node.next at this point, as it is now the last element.

Simply replace

                if temp_node.next == self.head:
                    self.tail == temp_node
                    self.tail.next = self.head

with

                if new_node.next is self.head:
                    self.tail = new_node

to get

class Node:
    def __init__(self,value):
        self.value = value
        self.next = None

class CircularSLL:

    def __init__(self):
        self.head = None
        self.tail = None

    def __iter__(self):
        node = self.head
        while node:
            yield node
            if node.next is self.head:
                break
            node = node.next

    def insertnode(self, value, location):
        new_node = Node(value)

        # check if head is None or not

        if self.head is None:
            self.head = new_node
            self.tail = new_node
            new_node.next = self.head

        else:
            # At the start
            if location == 0:
                new_node.next = self.head
                self.head = new_node
                self.tail.next = self.head

            # At the end
            elif location == -1:
                new_node.next = self.tail.next
                self.tail.next = new_node
                self.tail = new_node

            else:
                # At specific location
                temp_node = self.head
                index = 0

                while index < location - 1:
                    # node is the last element
                    if temp_node.next is self.head:
                        break
                    temp_node = temp_node.next
                    index  = 1

                next_node = temp_node.next
                new_node.next = next_node
                temp_node.next = new_node

                if new_node.next is self.head:
                    self.tail = new_node


            return 'The node has been successfully inserted'

cll = CircularSLL()

cll.insertnode(1,0)

cll.insertnode(3, 1)

cll.insertnode(4, 2)

cll.insertnode(5, 3)

cll.insertnode(6, 4)

cll.insertnode(10,0)

cll.insertnode(30, -1)

print([node.value for node in cll])

Output: [10, 1, 3, 4, 5, 6, 30]

I have also replaced == with is in several places to more clearly test for identity rather than equivalent values.