DSA/partition.py

#!/usr/bin/env python3
# vim: set ts=2 sw=2 et tw=80:

import sys
import random


def partition(A, begin, end):
  v_i = random.randrange(begin, end)
  v = A[v_i]
  A[v_i], A[end - 1] = A[end - 1], A[v_i]
  i = begin
  j = end - 2
  while j >= i:
    if A[j] > v:
      j = j - 1
    elif A[i] <= v:
      i = i + 1
    else:
      A[i], A[j] = A[j], A[i]
      j = j - 1
      i = i + 1
  A[i], A[end - 1] = A[end - 1], A[i]
  return i


def quicksort(A, begin, end):
  if begin < end - 1:
    i = partition(A, begin, end)
    print(A[begin:i], A[i], A[i + 1:end])
    quicksort(A, begin, i)
    quicksort(A, i + 1, end)
    print(A[begin:i], A[i], A[i + 1:end])


if __name__ == "__main__":
  args = [int(x) for x in sys.argv[1:]]
  print(args)
  quicksort(args, 0, len(args))
  print(args)