PYTHON PROGRAM • JSON, CSV & COLLECTIONS

Use a Double-ended Queue in Python

Learn use a double-ended queue in python with a short, executable Python example.

Intermediatedequeappendleftpopleft

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

[1, 2, 3, 4] 1

COMPLETE PYTHON PROGRAM

Complete Python implementation

from collections import deque
queue = deque([2, 3])
queue.appendleft(1)
queue.append(4)
print(list(queue), queue.popleft())

CURRENT STEP

Select Start to walk through the important lines.

SELECTED LINE

No line selected

EXPECTED OUTPUT FOR THE SAMPLE

[1, 2, 3, 4] 1

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Import the required standard-library tools and prepare the sample data for use a double-ended queue.
Apply deque and appendleft to compute the required result.
Display the result for use a double-ended queue and compare it with the documented sample output.

This example of use a double-ended queue computes the result directly from the prepared sample data. It demonstrates deque, appendleft, and popleft and prints a deterministic result that can be checked against the sample output.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

Check this

For use a double-ended queue, keep the data shape and value types consistent with deque.

Check this

Apply deque in the same order shown by the algorithm; changing the order can change the result.

Check this

Verify the final deque and appendleft result against the sample before trying new data.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.