Programming Interview Questions 9: Convert Array

Programming Interview Questions 9: Convert Array

Given an array [a1, a2, ..., aN, b1, b2, ..., bN, c1, c2, ..., cN]  convert it to [a1, b1, c1, a2, b2, c2, ..., aN, bN, cN] in-place using constant extra space

#!/usr/bin/python
#http://www.ardendertat.com/2011/10/18/programming-interview-questions-9-convert-array/

import sys

def geti(c, N):
  return (c%3) * N + c / 3

def convert(arr):
  N = len(arr) / 3
  callgeti = 0
  for i in range(len(arr)):
    j = geti(i, N)
    callgeti += 1
    while j < i:
      j = geti(j, N)
      callgeti += 1
    arr[i], arr[j] = arr[j], arr[i]
  return callgeti

def main():
  n = int(sys.argv[1])
  arr = [1] * n + [2] * n + [3] * n
  callgeti = convert(arr)
  print '%d/%d = %.2f\n' % (callgeti, n * 3, float(callgeti) / (n * 3))

if __name__ == '__main__': main()