HackerRank Collections.deque() Solution in Python

Why is deque used in Python?

I initially wondered, “Deque?” when I came across HackerRank’s Collections.deque() problem. It sounds like a science fiction device. It’s just a clever Python trick, though, and this challenge is a great way to hone your skills. Like we’re having coffee, I’ll walk you through it, sharing the code that worked for me and a few tips I learned along the way.

Alright, so what is a deque?

A deque, which is pronounced like “deck,” is an acronym for a double-ended queue. Think of a food truck line where you can pull burgers off the front or back or toss them onto either end. That is a deque! It functions similarly to a list, but it’s designed to be faster when working with both ends.

You are able:

Pull things off of either side and shove them onto the front or back.

All you need to get going is:

python

from collections import deque

For example, deques are excellent for tracking moves in a board game or managing your Netflix queue. They perform these tricks far more quickly than lists.

What Is the Topic of This HackerRank Problem?

Once you understand how to use Collections.deque(), the challenge is quite easy. Here’s what you’re doing:

You receive a number that indicates the number of commands you will be handling.
Commands such as pop, popleft, append, and appendleft will be used.
Lastly, print the contents of the deque in a single line, with spaces between each entry.

Python Code That Completes It

Here’s the code that helped me out in this situation. It is easy to use and very effective:

python

from collections import deque


n = int(input())


d = deque()


for _ in range(n):
    task = input().split()


    if task[0] == 'append':
        d.append(int(task[1]))


    elif task[0] == 'appendleft':
        d.appendleft(int(task[1]))


    elif task[0]  == 'pop':
        d.pop()


    elif task[0] == 'popleft':
        d.popleft()


print(*d)

The Step-by-Step Operation of This Code

Let’s dissect it as if we were going through an old CD stack:

• Grab the deque: importing a deque from collections is similar to taking your playlist app out of your pocket.
• How many commands?: n = int(input()) asks how many changes you’re making to the playlist. Like, how many songs are we messing with?
• Start with an empty deque: d = deque() sets up a blank deque. Keeps it nice and simple.
• Loop through the tasks: for _ in range(n) goes through each command. I used _ because I’m too lazy to count loops.
• Handle the tasks: task = input().split() turns each input (like append 5) into a list like [‘append’, ‘5’].
• Then:
  • append: Adds a number to the end of the deque, like queuing a song at the end of your playlist.
  • appendleft: Slips a number at the start, like putting a banger at the top.
  • Pop: Skips the final track or drops a number from the end.
  • popleft: Removes one from the start, like cutting the first song.

Play the last list: All of the numbers in the deque are displayed in a single line with spaces when print(*d) is used. Using the * is similar to pressing “play all” to view your entire playlist.

An Actual Case to Understand It

To make it very clear, here is an example:

Input:

6
append 1
append 2
appendleft 3
pop
popleft
append 4

Output:

1 4

• How to use a deque like it’s your best friend
• Handling input without wanting to chuck your laptop
• Fast queue tricks that feel like magic
• Nailing the exact output HackerRank wants

I still get a kick out of remembering when my code passed every test case. It’s like landing a perfect skate trick after falling a dozen times!

How Quick Is This Code?

• Time Complexity: Every operation (append, pop, etc.) is O(1). Compared to me running to catch the bus, that is faster!
  O(n) is the space complexity, where n is the number of numbers in your deque.

Deques are speedy because Python’s coders snuck in some genius behind-the-scenes stuff.

Keep Rocking the Code

Do you want to learn more? Here are a few places to visit:

• Python’s deque Guide

Related Post:

HackerRank Set pop(), remove(), and discard() Python Solution | In 7 Step-by-Step Explanation

HackerRank Python Solution – Using itertools combinations_with_replacement | In 5 Easy Steps

Conclusion:

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