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Write better code: Day 2 - Single Riffle Shuffle

arjunrajkumar profile image Arjun Rajkumar ・Updated on ・1 min read

This post originally appeared on Arjun Rajkumar 's blog. Arjun is a web developer based in Bangalore, India.


This was the previous question I solved today.

Day 2: Question 2

Write a method to tell us if a full deck of cards shuffled_deck is a single riffle of two other halves half1 and half2.

We'll represent a stack of cards as an array of integers in the range 1..52 (since there are 52 distinct cards in a deck).


Question from InterviewCake

If you want to follow along, feel free to post your answers in the comment.
My answers are in the comments.

Discussion (1)

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arjunrajkumar profile image
Arjun Rajkumar Author • Edited

Logic was to get the shuffled deck and check if the last card in shuffled deck belongs to the top of half 1 of half 2.

-do while loop until shuffled deck is empty.
-pick a card from the shuffled deck - check if it's the top card of half 1 or half2.
-if it matches top of half1 - pop it from half1, pop from deck.
-else if is top of half2, repeat.
-if the card does not match the top of either halves, it's not a single shuffle.


I think I could improve this. I am not sure yet what the complexity of using pop is.
If its always O[1] then this logic is good. But anyhow since the max deck of cards is always 52, change in performance wont make much difference even with better code than this.