Lecture Notes on 13 November 2009

# This function merges two sorted lists a and b 
def merge (a, b):
  c = []
  aIdx = 0
  bIdx = 0

  while ((aIdx < len(a)) and (bIdx < len(b))):
    if (a[aIdx] < b[bIdx]):
      c.append (a[aIdx])
      aIdx = aIdx + 1
    else:
      c.append (b[bIdx])
      bIdx = bIdx + 1

  while (aIdx < len(a)):
    c.append (a[aIdx])
    aIdx = aIdx + 1

  while (bIdx < len(b)):
    c.append (b[bIdx])
    bIdx = bIdx + 1

  return c

def main ():
  a = [1, 2, 5, 7, 9]
  b = [2, 3, 5, 8, 9, 11]
  c = merge (a, b)
  print c

main()



# Recursive code that implements the merge sort algorithm
def mergeSort (a, lo, hi):
  if (lo < hi):
    mid = (lo + hi) / 2
    mergeSort (a, lo, mid)
    mergeSort (a, mid + 1, hi)
    merge (a, lo, hi)