TITLE: Papers on arXiv solving the same problem at the same time
QUESTION [29 upvotes]: I am little bit curious about the following examples 

at least two papers appeared on arxiv at the same day solving one
  and the same problem.

Have you ever seen such a coincidence? If yes, can you provide the links to that papers? 

of course the papers maybe solving one and the same problem in a slightly different generalities, for example, one solved a certain case of the problem, and the other one solved the problem completely.
the authors should be different, for example, it is not allowed that  both papers have one and the same person as an author/co-author.

REPLY [3 votes]: This happened in 2013 in the context of finding $\epsilon$-approximate solutions to the maximum $s-t$ flow problem in near-linear-time (taking day to mean any 24 hour period).
The two references are https://arxiv.org/abs/1304.2338 (Jonathan A. Kelner, Yin Tat Lee, Lorenzo Orecchia, Aaron Sidford) and https://arxiv.org/abs/1304.2077 (Jonah Sherman).
As usual, the timing was not a coincidence.