Approximate Sorting

We show that any comparison based, randomized algorithm to approximate any given ranking of n items within expected Spearman's footrule distance n2/ν(n) needs at least n (min{log ν(n), log n} – 6) comparisons in the worst case. This bound is tight up to a constant factor since there exists a deterministic algorithm that shows that 6n(log ν(n)+1) comparisons are always sufficient.