Delete all the nodes from the list which are less than K

Given a Linked List and a key K. The task is to write a program to delete all the nodes from the list that are lesser than the key K.

**Examples:**

Input :12->15->9->11->5->6 K = 9Output :12 -> 15 -> 9 -> 11Input :13->4->16->9->22->45->5->16->6 K = 10Output :13 -> 16 -> 22 -> 45 -> 16

**Approach: **The approach is similar to deleting all nodes from the list which are greater than the given key.

There are two possible cases:

- Head node holds a value less than K: First check for all occurrences at head node which are lesser than ‘K’, delete them and change the head node appropriately.
- Some intermediate node holds value less than k: Start traversing from head and check if current node’s value is less than K. If yes then delete that node and move forward in the list.

Below is the implementation of the above approach:

`// C++ program to delete all the nodes from the list` `// that are lesser than the specified value K` `#include <bits/stdc++.h>` ` ` `using` `namespace` `std;` ` ` `// structure of a node` `struct` `Node {` ` ` `int` `data;` ` ` `Node* next;` `};` ` ` `// function to get a new node` `Node* getNode(` `int` `data)` `{` ` ` `Node* newNode = ` `new` `Node;` ` ` `newNode->data = data;` ` ` `newNode->next = NULL;` ` ` `return` `newNode;` `}` ` ` `// function to delete all the nodes from the list` `// that are lesser than the specified value K` `void` `deleteLesserNodes(Node** head_ref, ` `int` `K)` `{` ` ` `Node *temp = *head_ref, *prev;` ` ` ` ` `// If head node itself holds the value lessser than 'K'` ` ` `while` `(temp != NULL && temp->data < K) {` ` ` `*head_ref = temp->next; ` `// Changed head` ` ` `free` `(temp); ` `// free old head` ` ` `temp = *head_ref; ` `// Change temp` ` ` `}` ` ` ` ` `// Delete occurrences other than head` ` ` `while` `(temp != NULL) {` ` ` ` ` `// Search for the node to be deleted,` ` ` `// keep track of the previous node as we` ` ` `// need to change 'prev->next'` ` ` `while` `(temp != NULL && temp->data >= K) {` ` ` `prev = temp;` ` ` `temp = temp->next;` ` ` `}` ` ` ` ` `// If required value node was not present` ` ` `// in linked list` ` ` `if` `(temp == NULL)` ` ` `return` `;` ` ` ` ` `// Unlink the node from linked list` ` ` `prev->next = temp->next;` ` ` ` ` `delete` `temp; ` `// Free memory` ` ` ` ` `// Update Temp for next iteration of` ` ` `// outer loop` ` ` `temp = prev->next;` ` ` `}` `}` ` ` `// function to a print a linked list` `void` `printList(Node* head)` `{` ` ` `while` `(head) {` ` ` `cout << head->data << ` `" "` `;` ` ` `head = head->next;` ` ` `}` `}` ` ` `// Driver code` `int` `main()` `{` ` ` `// Create list: 12->15->9->11->5->6` ` ` `Node* head = getNode(12);` ` ` `head->next = getNode(15);` ` ` `head->next->next = getNode(9);` ` ` `head->next->next->next = getNode(11);` ` ` `head->next->next->next->next = getNode(5);` ` ` `head->next->next->next->next->next = getNode(6);` ` ` ` ` `int` `K = 9;` ` ` ` ` `cout << ` `"Initial List: "` `;` ` ` `printList(head);` ` ` ` ` `deleteLesserNodes(&head, K);` ` ` ` ` `cout << ` `"\nFinal List: "` `;` ` ` `printList(head);` ` ` ` ` `return` `0;` `}` |

**Output:**

Initial List: 12 15 9 11 5 6 Final List: 12 15 9 11

**Time Complexity:** O(N)