快排

QUICKSORT(A, p, r)
--if p<r
----q=PARTITION(A, p, r)
----QUICKSORT(A, q-1)
----QUICKSORT(A, q+1)

PARTITION(A, p, r)
--x=A[r]
--i=p-1
--for j=p to r-1
----if A[j]<=x
------i=i+1
------excahnge A[i] with A[j]
--exchange A[i+1] with A[r]
--return i+1

[p, i] v<=x
(i, j) v>x
[j, r-1] unknown