**to perform operations like insertion, deletion, sorting, searching on the linked list we need to find the reference to a particular node in a linked list.**

__operations on the linked list__so today we are going to learn how we can find the reference to the nodes to perform operations on a linked list.

__After completing this tutorial you are able to learn__- Reference to the last node
- Reference to second last node
- Reference to a node with particular info
- Reference to the predecessor of a node with particular info
- Reference to a node at a particular position

###
__Finding a reference to the last node__

as we know linked list contains the null or None value at the linked part of the last node of the list. so here is the code to find the reference to the last node of the linked list.

p = self.start while p.link is not None: p = p.link

__here we first store the reference of the first node of the list in p variable and then we continue to the next using the while loop till the value of link part of a node not equal to None.__

**Note:**###
__Finding a reference to the second last node__

here is the python code to find the reference to the second last node of the list.

p = self.start while p.link.link is not None: p = p.link

__here we run the while loop till the value of next to next link of the node equal to the null of None.__

**Note:**###
__Finding a reference to a node with particular info__

let's assume we need to find the node that contains the value x. for example, if we need to find the node that contains the value 30 then here is the python code to find the node with a particular value.

p = self.start while p is not None: if p.info == x: break p = p.link

__here we run the while loop till the last node of the list. and if we found the value of the node that equal to the value that we are searching then the break statement stops the while loop.__

**Note:**###
__Finding a reference to the predecessor of a node with particular info__

**predecessor node is the node before the node that contains the particular value. as you see in the image given below.**

__Predecessor:__

**here we need to find the reference to the predecessor of the node that contains the value x=30.**

__Note:__here is the python code to find the reference to the predecessor of the node with particular info.

p = self.start while p.link is not None: if p.link.info == x: break p = p.link

here we run the loop till the last node of the linked list and at every node, we check that if the info part of the next to next node is equal to the value x or not. if the value is equal to the x then we break the loop.

###
__Finding a reference to a node at a particular position__

Here we need to find the node at position 3 as you see in the image given above.

here is the python code to find the node at a particular position.

p = self.start i = 1 while i<k and p is not None: p = p.link i += 1

**here we run the while loop till the value of i is less than k and the last node to the list. and we increment the value of I at every iteration.**

__Note:__####
__Python program for traversing in the linked list.__

class Node: def __init__(self, value): self.info = value self.link = None class SingleLinkedList: def __init__(self): self.start = None def display_list(self): if self.start is None: print("List is empty") return else: print("List is : ") p = self.start while p is not None: print(p.info, " ", end=' ') p = p.link print() def count_nodes(self): p = self.start n = 0 while p is not None: n += 1 p = p.link print("Number of nodes in the list = ", n) def search(self): position = 1 p = self.start while p is not None: if p.info == x: print(x, " is at position ", position) return True position += 1 p = p.link else: print(x, " not found in list") return False def insert_in_beginning(self, data): temp = Node(data) temp.link = self.start self.start = temp def insert_at_end(self, data): temp = Node(data) if self.start is None: self.start = temp return p = self.start while p.link is not None: p = p.link p.link = temp def create_list(self): n = int(input("Enter the number of nodes : ")) if n == 0: return for i in range(n): data = int(input("Enter the element to be inserted : ")) self.insert_at_end(data) def insert_after(self, data, x): p = self.start while p is not None: if p.info == x: break p = p.link if p is None: print(x, "not present in the list") else: temp = Node(data) temp.link = p.link p.link = temp def insert_before(self, data, x): # If list is empty if self.start is None: print("List is empty") return if x == self.start.info: temp = Node(data) temp.link = self.start self.start = temp return p = self.start while p.link is not None: if p.link.info == x: break p = p.link if p.link is None: print(x, " not present in the list") else: temp = Node(data) temp.link = p.link p.link = temp def insert_at_position(self, data, k): if k == 1: temp = Node(data) temp.link = self.start self.start = temp return p = self.start i = 1 while i < k - 1 and p is not None: p = p.link i += 1 if p is None: print("You can insert only upto position", i) else: temp = Node(data) temp.link = p.link p.link = temp def delete_node(self, x): if self.start is None: print("List is empty") if self.start.info == x: self.start = self.start.link return p = self.start while p.link is not None: if p.link.info == x: break p = p.link if p.link is None: print("Element ", x , "not in list") else: p.link = p.link.link def delete_first_node(self): if self.start is None: return self.start = self.start.link def delete_last_node(self): if self.start is None: return if self.start.link is None: self.start = None return p = self.start while p.link.link is not None: p = p.link p.link = None def reverse_list(self): prev = None p = self.start while p is not None: next = p.link p.link = prev prev = p p = next self.start = prev def bubble_sort_exdata(self): end = None while end != self.start.link: p = self.start while p.link != end: q = p.link if p.info > q.info: p.info, q.info = q.info, p.info p = p.link end = p def bubble_sort_exlinks(self): end = None while end != self.start.link: r = p = self.start while p.link != end: q = p.link if p.info > q.info : p.link = q.link q.link = p if p != self.start: r.link = q else: self.start = q p,q = q,p r = p p = p.link end = p def has_cycle(self): if self.find_cycle() is None: return False else: return True def find_cycle(self): if self.start is None or self.start.link is None: return None slowR = self.start fastR = self.start while fastR is not None and fastR.link is not None: slowR = slowR.link fastR = fastR.link.link if slowR == fastR: return slowR return None def remove_cycle(self): c = self.find_cycle() if c is None: return print("Node at which the cycle was detected is ", c.info) p = c q = c len_cycle = 0 while True: len_cycle+=1 q = q.link if p == q: break print("Length of cycle is :", len_cycle) len_rem_list = 0 p = self.start while p != q: len_rem_list+=1 p = p.link q = q.link print("Number of nodes not included in the cycle are : ", len_rem_list) length_list = len_cycle + len_rem_list print("Length of the list is : ", length_list) p = self.start for i in range(length_list-1): p = p.link p.link = None def insert_cycle(self, x): if self.start is None: return p = self.start px = None prev = None while p is not None: if p.info == x: px = p prev = p p = p.link if px is not None: prev.link = px else: print(x, " not present in list") def merge2(self, list2): merge_list = SingleLinkedList() merge_list.start = self._merge2(self.start, list2.start) return merge_list def _merge2(self, p1, p2): if p1.info <= p2.info: startM = p1 p1 = p1.link else: startM = p2 p2 = p2.link pM = startM while p1 is not None and p2 is not None: if p1.info <= p2.info: pM.link = p1 pM = pM.link p1 = p1.link else: pM.link = p2 pM = pM.link p2 = p2.link if p1 is None: pM.link = p2 else: pM.link = p1 return startM def merge_sort(self): self.start = self._merge_sort_rec(self.start) def _merge_sort_rec(self, list_start): if list_start is None or list_start.link is None: return list_start start1 = list_start start2 = self._divide_list(list_start) start1 = self._merge_sort_rec(start1) start2 = self._merge_sort_rec(start2) startM = self._merge2(start1, start2) return startM def _divide_list(self, p): q = p.link.link while q is not None and q.link is not None: p = p.link q = q.link.link start2 = p.link p.link = None return start2 ########################## list = SingleLinkedList() list.create_list() while True: print("1. Display list") print("2. Count the number of nodes") print("3. Search for an element") print("4. Insert in empty list/insert in beginning of the list") print("5. Insert a node at the end of the list") print("6. Insert a node after a specified node") print("7. Insert a node before a specified node") print("8. Insert a node at a given position") print("9. Delete first node") print("10. Delete last node") print("11. Delete any node") print("12. Reverse the list") print("13. Bubble sort by exchanging data") print("14. Bubble sort by exchanging links") print("15. Merge sort") print("16. Insert Cycle") print("17. Detect Cycle") print("18. Remove Cycle") print("19. Quite") option = int(input("Enter your choice")) if option == 1: list.display_list() elif option == 2: list.count_nodes() elif option == 3: data = int(input("Enter the element to be searched : ")) list.search(data) elif option == 4: data = int(input("Enter the element to be inserted : ")) list.insert_in_beginning(data) elif option == 5: data = int(input("Enter the element to be inserted : ")) list.insert_at_end(data) elif option == 6: data = int(input("Enter the element to be inserted : ")) x = int(input("Enter the element after which to insert : ")) list.insert_after(data, x) elif option == 7: data = int(input("Enter the element to be inserted : ")) x = int(input("Enter the element before which to insert : ")) list.insert_before(data, x) elif option == 8: data = int(input("Enter the element to be inserted : ")) k = int(input("Enter the position at which to insert : ")) list.insert_at_position(data, k) elif option == 9: list.delete_first_node() elif option == 10: list.delete_last_node() elif option == 11: data = int(input("Enter the element to be deleted : ")) list.delete_node(data) elif option == 12: list.reverse_list() elif option == 13: list.bubble_sort_exdata() elif option == 14: list.bubble_sort_exlinks() elif option == 15: list.merge_sort() elif option == 16: data = int(input("Enter the element at which the cycle has to be inserted : ")) list.insert_cycle(data) elif option == 17: if list.has_cycle(): print("List has a cycle") else: print("List does not have a cycle") elif option == 18: list.remove_cycle() elif option == 19: break else: print("Wrong option") print()

Also, read other tutorials as well

- What are Data Structures and algorithms
- Algorithm design and analysis
- Classification of algorithms
- How to calculate the running time of an algorithm.
- Worst Average and Best-case analysis of the algorithm.
- Big o notation
- Big o notation examples
- Linked List in Data Structures
- Traversing in Linked list
- Insertion in the linked list
- Deletion in a linked list
- Reversing a linked list
- Sorting a linked list
- Find and remove the loop in the linked list
- Doubly linked list
- Insertion in the doubly linked list
- Deletion in the doubly linked list
- Reversing a doubly linked list
- Circular linked list
- Insertion in the circular linked list
- Deletion in the circular linked list
- Merge two linked list
- Header linked list
- Sorted linked list
- Stack in data structures
- Queue in data structures
- Circular queue
- Dequeue in the data structure
- Priority queue
- Polish notation
- Tree in the data structure
- Binary tree
- Array representation of the binary tree
- linked representation of a binary tree
- Traversing in the binary tree
- Inorder traversal in the binary tree
- Preorder traversal in the binary tree
- Postorder traversal in the binary tree
- Level order traversal in the binary tree
- Binary search tree
- Insertion in the binary search tree
- Deletion in the binary search tree
- Heap in data structures

## 0 Comments