Getting Started with Competitive Programming
(an NPTEL course)
Module A. Prerequisites
1. Single-Source Shortest Paths
If you are interested in learning thee proofs of the algorithms we discuss, you could take a a look at this chapter.
For SSSP, you can also try out this visualgo module.
2. All-Pairs Shortest Paths
We describe the algorithm described in Section 9.8 in this chapter. It's readable stand alone, but you could read the whole chapter if you want to experience a natural build-up to the ideas of the final algorithm :)