The problem of largest K values

http://www.mitbbs.com/article_t/JobHunting/31297671.html

"Give efficient algorithms for finding the largest k values (in order) out of a set of n, using comparisons only (e.g. no hashing), in the case where: (a) k = 3 (b) k = n/2; (c) k = log(n). (You can use a different algorithm for each case.) State the asymptotic worst-case running time of your algorithms. "