import random

def partition(list, first, last):
    pval = list[first]
    h = first
    for k in range(first+1,last+1):
        if list[k] < pval:
            h = h+1
            (list[h],list[k]) = (list[k],list[h]) # swap!
    (list[first],list[h]) = (list[h],list[first]) # swap!
    return h

def partition2(list, first, last):
    i = first
    j = last+1
    pval = list[first]
    while True:
        while True:
            i = i+1
            if i > last or list[i] >= pval: break
        while True:
            j = j-1
            if list[j] <= pval: break
        if i < j:
            (list[i],list[j]) = (list[j],list[i]) # swap
        else:
            break
    (list[first],list[j]) = (list[j],list[first]) # swap
    return j
            

def quicksort(list, first, last):
    if first < last:
        p = partition2(list, first, last)
        #print 'quicksort(', first, ',', last, '), p =', p
        quicksort(list, first, p-1)
        quicksort(list, p+1, last)
    return

# creates a random list
def random_list(n, min=0, max=9):
    list = [] # empty list
    for i in range(n):
        list.append( random.randint(min, max) )
    return list

def insertion_sort(list):
    n = len(list)
    for i in range(1,n):
        val = list[i]
        j = i-1
        while j >= 0 and val < list[j]:
            list[j+1] = list[j]
            j = j-1
        list[j+1] = val
    return

def test_partition():
    while True:
        list = raw_input("Enter a list (or q to quit): ")
        if list == 'q':  break
        list = eval(list)
        print list
        p = partition(list, 0, len(list)-1)
        print list
        print "Partition returns:", p
    return

def main():
    #list = input('Enter the list: ')
    list = random_list(16, -9, 9)
    print list
    quicksort(list, 0, len(list)-1)
    print list
    test_partition()
    return
    # testing for merge (ran this first)
    # list = [ 1, 5, 6, 2, 3, 9 ]
    # merge(list, 0, 2, 5)
    # print list
    
    
main()