Merge 2 Sorted Linked List in c++

 

Merging two sorted linked lists in C++ is a common task that can be accomplished using a variety of techniques. The most common approach is to use a recursive algorithm that compares the first elements of each list and then recursively calls itself to merge the remaining elements. Another approach is to use an iterative algorithm that repeatedly compares the first elements of each list and appends the smaller element to a new list until one of the lists is exhausted.

One of the key advantages of using a linked list data structure is that it allows for efficient insertion and deletion of elements at any position in the list. This makes it an ideal choice for sorting and merging large datasets. However, when it comes to merging two sorted linked lists, the process can be somewhat complex, particularly when dealing with large lists or when the lists are not already sorted.

One common approach to merging two sorted linked lists is to use a recursive algorithm. This approach compares the first elements of each list and then recursively calls itself to merge the remaining elements. The base case for this algorithm is when one of the lists is empty, in which case the remaining list is simply returned.

Here is an example of a recursive algorithm for merging two sorted linked lists in C++:

// Helper function for merging two sorted linked lists 
 ListNode* merge(ListNode* l1, ListNode* l2) { 
 // Base case: one of the lists is empty 
 if (!l1) return l2;
    if (!l2) return l1; 
 // Compare the first elements of each list 
 if (l1->val <= l2->val) { 
 // Append the smaller element to the merged list
 
        l1->next = merge(l1->next, l2);
 return l1;
 } else {
         
// Append the smaller element to the merged list 
 l2->next = merge(l1, l2->next);
 return l2; 
 } 
}

This recursive approach has a time complexity of O(n log n) where n is the total number of elements in both lists. This is because the algorithm repeatedly divides the list in half until it reaches the base case of one of the lists being empty.

Another approach to merging two sorted linked lists is to use an iterative algorithm. This approach repeatedly compares the first elements of each list and appends the smaller element to a new list until one of the lists is exhausted. The key advantage of this approach is that it has a time complexity of O(n) where n is the total number of elements in both lists. This is because the algorithm only needs to iterate through each element once.

Here is an example of an iterative algorithm for merging two sorted linked lists in C++:

// Helper function for merging two sorted linked lists 
ListNode* merge(ListNode* l1, ListNode* l2) {
 // Create a new dummy node for the merged list
 
    ListNode dummy(0);
    ListNode* curr = &dummy;
 // Iterate through each element in both lists 
 while (l1 && l2) {
        if (l1->val <= l2->val) { 
 // Append the smaller element to the merged list 
 curr->next = l1;
            l1 = l1->next;
 } 
else { 
 // Append the smaller element to the merged list 
 curr->next = l2;
            l2 =