这种划分在快速排序中也用到了:

#py2.7#coding:utf-8import randomdef findkth(ll, k):    if k > len(ll):        raise Exception('Argument error')    else:        pivot = ll[random.randrange(0,len(ll))]        last = 0        for i in range(1, len(ll)):            if ll[i] >= pivot:                last += 1                swap(ll, i, last)        swap(ll, 0, last)        print(ll,k)        order = last+1        if order == k:            return pivot        elif order < k:            return findkth(ll[last + 1:], k - order)        else:            return findkth(ll[0:last], k)def swap(ll, i, last):    tmp = ll[i]    ll[i] = ll[last]    ll[last] = tmpll = [1, 22, 31, 14, 0.5, 26, 17, 38, 19, 310]k = 3print(findkth(ll, k))