longest_common_binary.py

def substr_in_all(arr, part):
  for dna in arr:
    if dna.find(part)==-1:
      return False
  return True

def common_substr(arr, l):
  first = arr[0]
  for i in range(len(first)-l+1):
    part = first[i:i+l]
    if substr_in_all(arr, part):
      return part
  return ""

def longest_common_substr(arr):
  l = 0; r = len(arr[0])

  while l+1<r:
    mid = (l+r) / 2
    if common_substr(arr, mid)!="":
        l=mid
    else:
        r=mid

  return common_substr(arr, l)


arr=['abdercaagcd','decaaagcaeder','acderaacdgg']

print longest_common_substr(arr)