Tri quicksort

quicksort.py

# quicksort implementation
# based on:
#   http://me.dt.in.th/page/Quicksort/

import random

def quicksort(a, start=0, end=None):
    # first pass of the algorithm?
    if end is None:
        end = len(a) - 1
    
    # one element is always sorted!
    if start >= end:
        return

    # pick random pivot, swap with first element
    pivot = random.randint(start, end)
    
    a[pivot], a[start] = a[start], a[pivot]
    pivot = start
    
    # partition from first element
    last = start
    for i in range(start + 1, end + 1):
        if(a[i] < a[pivot]):
            last += 1
            a[i], a[last] = a[last], a[i]
    
    a[pivot], a[last] = a[last], a[pivot]
    pivot = last
    
    # run the algorithm on the two subpartitions (pivot excluded as it is sorted)
    quicksort(a, start, pivot - 1)
    quicksort(a, pivot + 1, end)

# test
array = random.sample(range(10), 10)

print(array)
quicksort(array)
print(array)