Python Program For Inserting Node In The Middle Of The Linked List
Given a linked list containing n nodes. The problem is to insert a new node with data x at the middle of the list. If n is even, then insert the new node after the (n/2)th node, else insert the new node after the (n+1)/2th node.
Examples:
Input : list: 1->2->4->5
x = 3
Output : 1->2->3->4->5
Input : list: 5->10->4->32->16
x = 41
Output : 5->10->4->41->32->16
Method 1(Using length of the linked list):
Find the number of nodes or length of the linked using one traversal. Let it be len. Calculate c = (len/2), if len is even, else c = (len+1)/2, if len is odd. Traverse again the first c nodes and insert the new node after the cth node.
- Python3
Python3
# Python3 implementation to insert node# at the middle of a linked list# Node classclass Node: # constructor to create a new node def __init__(self, data): self.data = data self.next = None# function to insert node at the# middle of linked list given the headdef insertAtMid(head, x): if(head == None): #if the list is empty head = Node(x) else: # create a new node for the value # to be inserted newNode = Node(x) ptr = head length = 0 # calculate the length of the linked # list while(ptr != None): ptr = ptr.next length += 1 # 'count' the number of node after which # the new node has to be inserted if(length % 2 == 0): count = length / 2 else: (length + 1) / 2 ptr = head # move ptr to the node after which # the new node has to inserted while(count > 1): count -= 1 ptr = ptr.next # insert the 'newNode' and adjust # links accordingly newNode.next = ptr.next ptr.next = newNode# function to display the linked listdef display(head): temp = head while(temp != None): print(str(temp.data), end = " ") temp = temp.next# Driver Code# Creating the linked list 1.2.4.5head = Node(1)head.next = Node(2)head.next.next = Node(4)head.next.next.next = Node(5)print("Linked list before insertion: ", end = "")display(head)# inserting 3 in the middle of the linked list.x = 3insertAtMid(head, x)print("Linked list after insertion: " , end = "")display(head)# This code is contributed by Pranav Devarakonda |
Output:
Linked list before insertion: 1 2 4 5 Linked list after insertion: 1 2 3 4 5
Time Complexity: O(n)
Space complexity: O(n) where n is the number of nodes in a linked list
Method 2(Using two pointers):
Based on the tortoise and hare algorithm which uses two pointers, one known as slow and the other known as fast. This algorithm helps in finding the middle node of the linked list. It is explained in the front and black split procedure of this post. Now, you can insert the new node after the middle node obtained from the above process. This approach requires only a single traversal of the list.
- Python3
Python3
# Python implementation to insert node # at the middle of the linked list # Node Classclass Node : def __init__(self, d): self.data = d self.next = None class LinkedList: # function to insert node at the # middle of the linked list def __init__(self): self.head = None # Function to insert a new node # at the beginning def push(self, new_data): new_node = Node(new_data) new_node.next = self.head self.head = new_node def insertAtMid(self, x): # if list is empty if (self.head == None): self.head = Node(x) else: # get a new node newNode = Node(x) # assign values to the slow # and fast pointers slow = self.head fast = self.head.next while (fast != None and fast.next != None): # move slow pointer to next node slow = slow.next # move fast pointer two nodes # at a time fast = fast.next.next # insert the 'newNode' and # adjust the required links newNode.next = slow.next slow.next = newNode # function to display the linked list def display(self): temp = self.head while (temp != None): print(temp.data, end = " "), temp = temp.next# Driver Code# Creating the list 1.2.4.5 ll = LinkedList()ll.push(5)ll.push(4)ll.push(2)ll.push(1)print("Linked list before insertion: "),ll.display()x = 3ll.insertAtMid(x)print("Linked list after insertion: "),ll.display()# This code is contributed by prerna saini |
Output:
Linked list before insertion: 1 2 4 5 Linked list after insertion: 1 2 3 4 5
Time Complexity: O(n)
Space complexity: O(n) where n is size of linked list
Please refer complete article on Insert node into the middle of the linked list for more details!
