Median of Medians (BFPRT): Finding the k-th Smallest in Worst-Case Linear Time
How the PICK algorithm from the 1973 paper by Blum, Floyd, Pratt, Rivest, and Tarjan selects the k-th smallest value in worst-case linear time, and where the group size of five comes from.
algorithmsselectionmedian-of-medianscomplexity