Insertion Sort for Singly Linked List

Given a singly linked list, the task is to sort the list (in ascending order) using the insertion sort algorithm.

Examples:

Input: 5->4->1->3->2
Output: 1->2->3->4->5

Input: 4->3->2->1
Output: 1->2->3->4

The prerequisite is Insertion Sort on Array. The idea is to gradually build a sorted portion of the list within the same memory space as the original list.

Step-by-step approach:

• Start with an initially empty "sorted" list, which will be built by rearranging nodes from the original list.
• Traverse the original linked list one node at a time.
  • For each node, find its correct position within the "sorted" portion of the list.
  • If the node should be placed at the beginning (i.e., it's smaller than the first node in the sorted list), it becomes the new head of the sorted list.
  • Otherwise, traverse the sorted list to find the correct position and insert the node there.
• Continue this process until all nodes from the original list have been repositioned in the sorted order
• Return the head of sorted list.

Below is the implementation of the above approach

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Time Complexity: O(n²), In the worst case, we might have to traverse all nodes of the sorted list for inserting a node.
Auxiliary Space: O(1), No extra space is required