"""
Some versions of the "Look and Say" sequence, you can find it into the The
On-Line Encyclopedia of Integer Sequences, as sequence A005150:
http://www.research.att.com/~njas/sequences/A005150

V1.1, by leonardo maffi, Dec 24 2006
"""

# http://www.research.att.com/~njas/sequences/A005150

# Short self-contained version
from itertools import groupby
def A005150a(n, s=(1,)):
  for i in range(n-1):
    s+= (int("".join( `len(list(g))`+str(h) for h,g in groupby(str(s[-1])) )),)
  return s


# Generator version
from itertools import groupby
def A005150b(n, s=1):
  yield s
  for i in range(n-1):
    s = int("".join( `len(list(g))`+str(h) for h,g in groupby(str(s)) ))
    yield s


# Infinite generator version
from itertools import groupby
def A005150c(s=1):
  yield s
  while True:
    s = int("".join( `len(list(g))`+str(h) for h,g in groupby(str(s)) ))
    yield s


def A005150d(n): # faster uncompiled
    strl = {("1","1","1"): "31", ("1","1"): "21", ("1",): "11",
            ("2","2","2"): "32", ("2","2"): "22", ("2",): "12",
            ("3","3","3"): "33", ("3","3"): "23", ("3",): "13" }
    result = [1]
    prec = "1"
    for i in xrange(n-1):
        prec = "".join( strl[tuple(l)] for e,l in groupby(prec) )
        result.append( int(prec) )
    return result


def A005150e(n): # faster compiled with Psyco
    strl = {("1","1","1"): "31", ("1","1"): "21", ("1",): "11",
            ("2","2","2"): "32", ("2","2"): "22", ("2",): "12",
            ("3","3","3"): "33", ("3","3"): "23", ("3",): "13" }
    s = [1]
    prec = str(s[-1])
    for i in xrange(n-1):
        r = []
        for e,l in groupby(prec):
            r.append( strl[tuple(l)] )
        prec = "".join(r)
        s.append( int(prec) )
    return s


try:
    import psyco
    psyco.bind(A005150e)
except ImportError:
    pass


# Short version that uses nestlist
from itertools import groupby
f = lambda s: int("".join( `len(list(g))`+str(h) for h,g in groupby(str(s)) ))
A005150f = lambda n: nestlist(f, n-1, 1)


# Shorter version that uses nestlist
import itertools as i;A=lambda n:nestlist(lambda s:int("".join(`len(list(g))`+str(h)for h,g in i.groupby(str(s)))),n-1,1)


# Where:
def nestlist(f, n, seed):
  result = [seed]
  for i in xrange(n):
    result.append( f(result[-1]) )
  return result

from itertools import islice
print A005150a(15), "\n"
print list(A005150b(15)), "\n"
print list(islice(A005150c(), 15)), "\n"
print A005150d(15), "\n"
print A005150e(15), "\n"
print A005150f(15), "\n"
print A(15)

print "----------------------------"
print "Few timings:"
from time import clock

n = 32

t = clock()
A005150a(n)
print round(clock() - t, 2)

t = clock()
A005150d(n)
print round(clock() - t, 2)

t = clock()
A005150e(n) # With psyco
print round(clock() - t, 2)