Expected Time Bounds for Selection
A new selection algorithm is presented which
is shown to be very efficient on the average, 
both theoretically and practically.  The number of comparisons
used to select the ith smallest of n numbers 
is n+min(i,n-i)+o(n).  A lower bound within 9
percent of the above formula is also derived.
CACM March, 1975
Floyd, R. W.
Rivest, R. L.
