DSA · Theory

Quicksort on Doubly Linked List

Theory

192/810

Quicksort on Doubly Linked List

Quicksort 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 Quicksort on Doubly Linked List.

From the example next to this theory: Quicksort on Doubly Linked List — quick sort partitions around a pivot, then sorts both sides.

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

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

Diagram

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

Exam tip

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

Example

def quick_sort(arr):
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) // 2]
    left = [x for x in arr if x < pivot]
    mid = [x for x in arr if x == pivot]
    right = [x for x in arr if x > pivot]
    return quick_sort(left) + mid + quick_sort(right)

print(quick_sort([5, 1, 4, 2, 3]))

Quicksort on Doubly Linked List — quick sort partitions around a pivot, then sorts both sides.

Short notes

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

DSA · Theory

Quicksort on Doubly Linked List

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Theory

192/810

Quicksort on Doubly Linked List

Quicksort 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 Quicksort on Doubly Linked List.

From the example next to this theory: Quicksort on Doubly Linked List — quick sort partitions around a pivot, then sorts both sides.

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

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

Diagram

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

Exam tip

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

Example

def quick_sort(arr):
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) // 2]
    left = [x for x in arr if x < pivot]
    mid = [x for x in arr if x == pivot]
    right = [x for x in arr if x > pivot]
    return quick_sort(left) + mid + quick_sort(right)

print(quick_sort([5, 1, 4, 2, 3]))

Quicksort on Doubly Linked List — quick sort partitions around a pivot, then sorts both sides.

Short notes

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

Quicksort on Doubly Linked List

Example

Short notes

Questions

Quicksort on Doubly Linked List

Example

Short notes

Questions