Dijkstra
A swift based implementation of the Dijkstra algorithm
Purpose
The goal of this implementation is first for me to have a hand on the swift language, but also I wanted to compare the perfomance with an Objective C implementation.
Algorithm presentation
It's the basic Dijkstra algorithm as you can check on Wikipedia. The only change I have made is that edges can have multiple weights (for exemple in a road, first might be the state of the road (good,bad etc..) and another one the actual distance). You can contact me if you have questions about it.
Data input
I generate a binary tree created by the method func createGraph(graph: Graph,root: Vertex, level: Int). The level represents the number of levels in the tree.
As a result, the algorithm will always find the way through the entire tree, it's the worst case scenario.
Comparison with ObjC
The results are quite deceiving, as Apple mentions that swift will be like 2.8x faster that ObjC. You can find the exact same implementation of the algorithm, with the same change on the weight of the edges, here
Here are the results :
| Level | Objective C impl | Swift Impl |
|---|---|---|
| 2 (8 nodes) | 0.1ms | 3ms |
| 5 (64 nodes) | 3ms | 70ms |
| 10 (2048 nodes) | 1950ms | 55000ms |
| 12 (8192 nodes) | 30000ms | ... |
The tests are being run in the simulator, so it might not be very exact even if I run them multiple times. It's not a very scientific proof, but as the results are quite different, we can say without too much risk that the swift implementation takes much longer to execute.
As it's a new feature, I hope in the future release of Xcode they will improve perfomance, but for the moment I'm a bit disappointed...
Note: Following this tweet the tests were run with the -OFast optimization flag
Roadmap
- Add test in the code, for instance if all the edges don't have the same distances dimension, it will crash
- Adding unit test
Tools/Versions
- Xcode 6
- iPhone Simulator iPhone 4s/iOS 8
- Coffee
Licence
[Apache licence 2.0](http://www.tldrlegal.com/license/apache-license-2.0-(apache-2.0)
Please send me an email if you use this julien.gomes@gmail.com
Follow me on twitter @juliengomes