By Donald E. Knuth
Communications of the ACM,
Vol. 6 No. 11, Pages 685-688
Detailed statistics are given on the length of maximal sorted strings which result from the first (internal sort) phase of a merge sort onto tapes. It is shown that the strings produced by an alternating method (i.e. one which produces ascending and descending strings alternately) tend to be only three-fourths as long as those in a method which produces only ascending strings, contrary to statements which have appeared previously in the literature. A slight modification of the read-backward polyphase merge algorithm is therefore suggested.
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