# 399: Travelling Salesman Problem

## Explanation

The Travelling salesman problem is a classic problem in computer science that given a list of cities and their pairwise distances, the task is to find the shortest possible route that visits each city exactly once and returns to the origin city. A naive solution solves the problem in n! time (where n is the size of the list), simply by checking all possible routes, and selecting the shortest one. The first algorithms solving this problem for higher values of n is measured by (n^{2}2^{n}), but in Math it's only faster but not exact.

The joke is that the computer salesman selling on eBay does not have to worry about this problem since he does not need to travel, to which the travelling salesman angrily responds "shut the hell up".

The title text wonders about the time complexity of the Cutting-plane method, which is sometimes used to solve optimization problems. The last sentence suggests the down side for Randall of writing comics about computer science; he sometimes encounters problems to which he cannot find the answer, whereas authors of simpler comics such as Garfield do not have this problem. This is also likely a reference to 78: Garfield, which parodies Garfield's simplicity.

This is so far the only comic featuring the Brown Hat character.

Also see previous strip 287: NP-Complete.

## Transcript

- [There is a linked black web, with a path in red; it may be a map of the USA.]
- Brute-force solution:O(n!)
- [The web continues in this one. A man with a hat and a case is drawing it.]
- Dynamic programming algorithms: O(n
^{2}2^{n}) - [Another man, with a hat too, is at a computer, looking back over the chair.]
- Selling on eBay: O(1)
- Computer salesman: Still working on your route?
- Drawing salesman: Shut the hell up.

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# Discussion

Does anyone remember if the Brown Hat appears in any other comics?

- I'm not sure, so I created a category and page for him, let's see if that catches any others. --
**Jeff**(talk) 22:04, 29 March 2013 (UTC)- According to the transcript we have two different Brown Hat Guys here. I'm working on this.--Dgbrt (talk) 21:49, 5 October 2013 (UTC)
- I'm inclined to think that Brown Hat is specific to this comic, the brown hat being the 50's style homburg or fedora common to salesmen trying to look respectable... Randall likely added the hats to depict folks from a bygone era, (one of whom has caught up with the trend.) -- IronyChef (talk) 01:49, 10 January 2014 (UTC)

- According to the transcript we have two different Brown Hat Guys here. I'm working on this.--Dgbrt (talk) 21:49, 5 October 2013 (UTC)

It's probably not in the least important, but the network appears to be a collection of key cities in the US arranged by geographical location. 130.160.145.185 23:07, 9 March 2013 (UTC)

added a better explanation of the title text. -- Nick,5 Oct 2013 69.193.7.67 (talk) *(please sign your comments with ~~~~)*

Has anyone answered the question in the title text? --Ricketybridge (talk) 23:55, 9 January 2014 (UTC)

- "it is bitter news that in the forty years since Held and Karp no better guarantee [than n^2.2^n] has been found for the problem" [1]. So whereas linear programming techinques tend to be quicker than other algorithms, they have not been shown to be better than O(n^2.2^n).141.101.98.55 17:05, 17 August 2014 (UTC)

Doesn't someone at ebay still have to solve the TSP? I guess that's the entire point though. 141.101.85.223 08:48, 27 July 2014 (UTC)

- No because you can send your sales information to all customers at once because they come to you, electronically. It takes no longer for you to be viewed by 100 people than by one person. Thus O(1). 141.101.98.55 17:05, 17 August 2014 (UTC)
- I never used ebay so I don't know how it works and I'm probably missing something obvious. (Maybe it should be explained at the explanation?) If you wanted to personally sell about 17 items to 17 cities like the guy on the left, you have to visit each city by car or something. How does ebay visit the 17 cities to send the items?141.101.85.199 06:34, 19 August 2014 (UTC)