Sign In

Communications of the ACM

Research highlights

Technical Perspective: Can Data Structures Treat Us Fairly?

interior framing of a house

Credit: Getty Images

When asked to pick a random buddy from our Facebook friends list, we may struggle since our nomination is likely to be biased toward individuals with whom we interact more frequently. Computer assistance in such a case would make things easier: we can just store our friends' names in an array. Whenever a query comes, the computer generates a random array index and returns the name stored in the corresponding location. The question now is whether, for any given data structure problem, we can build a data structure that generates "fair" output while maintaining query efficiency.

In the context of data structure query-answering, fairness can be defined as follows: we either return all valid answers or just return a uniformly random one. Although this definition does not capture all human expectations of fairness, it is the most natural one for data structures from a technical sense. The challenge is that returning all valid answers may be time prohibitive, while returning a uniformly random one in a timely manner could also be difficult due to specific data storage orders and query-answering procedures. Consider the problem of finding red nodes in a binary tree with half of the nodes colored red and the other half blue. We can certainly use our favorite tree traversal algorithms, such as breadth-first search, to find all red nodes in the tree, but doing so will take time proportional to the size of the tree. We can also take random root-leaf paths to find one red node; this approach is much more time-efficient, but it favors red nodes closer to the root, resulting in an output that is not uniformly random.


No entries found

Log in to Read the Full Article

Sign In

Sign in using your ACM Web Account username and password to access premium content if you are an ACM member, Communications subscriber or Digital Library subscriber.

Need Access?

Please select one of the options below for access to premium content and features.

Create a Web Account

If you are already an ACM member, Communications subscriber, or Digital Library subscriber, please set up a web account to access premium content on this site.

Join the ACM

Become a member to take full advantage of ACM's outstanding computing information resources, networking opportunities, and other benefits.

Subscribe to Communications of the ACM Magazine

Get full access to 50+ years of CACM content and receive the print version of the magazine monthly.

Purchase the Article

Non-members can purchase this article or a copy of the magazine in which it appears.