A Selection Tree for Merging Large Number of Lists
The K-Way Merging Algorithm just described works well if k < 8. Otherwise, the number of comparisons needed to find the minimum value each step of the way is very large.
Instead, it is easier to use a selection tree which allows us to determine a minimum key value more quickly.
Merging k lists using this method is related to log2 k (the depth of the selection tree) rather than to k.
Updating selection trees is not easy ==> Keep a tree of losers (Knuth, 73).