Memory-efficient way of computing the median of a large data set? [closed]

Question

If one computer can only hold 1 million numbers, how to find out the median number from 100 million numbers?

Answer 1

Reduce the problem to a more difficult one: sort the 100 million numbers using merge sort Then, take the 50 millionth element.

Answer 2

Do an external sort and then scan once for the median.

Hopefully, the real problem was "how do I do an external sort"? (If this is homework...I want to help in the right way. :-)