DSA · Theory

Merge Sort on Doubly Linked List

Theory

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Merge Sort on Doubly Linked List

Merge Sort on Doubly Linked List is a DSA topic. In plain words you use it for a ticket queue node in a counter. Don’t start with a slogan — start with that picture.

Smallest example: head → next → …. Type it, run it, and say what you see. If you can do that from memory, you know Merge Sort on Doubly Linked List.

From the example next to this theory: Merge Sort on Doubly Linked List — merge sort divides the array, sorts halves, then merges — O(n log n).

Trap — losing the next pointer on delete. Fix that before you talk about advanced DSA.

Viva — what is Merge Sort on Doubly Linked List? Then show head → next → …. Then name the trap.

Diagram

  [10] → [20] → [30] → /
   head              tail

Exam tip

What is Merge Sort on Doubly Linked List? Show this: head → next → …. Trap: losing the next pointer on delete.

Example

def merge_sort(arr):
    if len(arr) <= 1:
        return arr
    mid = len(arr) // 2
    left = merge_sort(arr[:mid])
    right = merge_sort(arr[mid:])
    out, i, j = [], 0, 0
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            out.append(left[i]); i += 1
        else:
            out.append(right[j]); j += 1
    return out + left[i:] + right[j:]

print(merge_sort([5, 1, 4, 2]))

Merge Sort on Doubly Linked List — merge sort divides the array, sorts halves, then merges — O(n log n).

Short notes

DefMerge Sort on Doubly Linked List — a ticket queue node in a counter.
Rulehead → next → …
Traplosing the next pointer on delete
Usea counter

def merge_sort(arr): if len(arr) <= 1: return arr mid = len(arr) // 2 left = merge_sort(arr[:mid]) right = merge_sort(arr[mid:]) out, i, j = [], 0, 0 while i < len(left) and j < len(right): if left[i] <= right[j]: out.append(left[i]); i += 1 else: out.append(right[j]); j += 1 return out + left[i:] + right[j:] print(merge_sort([5, 1, 4, 2]))

Merge Sort on Doubly Linked List

Example

Short notes

Questions

Merge Sort on Doubly Linked List

Example

Short notes

Questions