Look and Say

lookandsay.py

import sys

SENTINEL = -1


def lookandsay(num):
    """Return the look and say version of num."""

    num = str(num)

    cur_digit = SENTINEL
    cur_streak = 0

    result = ""

    for cur in num:

        if cur == cur_digit or cur_digit == SENTINEL:
            cur_streak += 1
        else:

            result += str(cur_streak)
            result += str(cur_digit)

            cur_streak = 1

        cur_digit = cur

    result += str(cur_streak)
    result += str(cur_digit)

    return result


def lookandsay_sequence(num_items):
    """Print the first num_items of the look an say sequence."""

    cur = 1

    for i in range(num_items):
        print cur
        cur = lookandsay(cur)


if __name__ == "__main__":
    if len(sys.argv) > 1:
        print lookandsay(sys.argv[1])
    else:
        lookandsay_sequence(10)

Nice. Pretty sure this works.

Here is mine:

def look_and_say(digits):
    outStr = ""

    if not digits:
        return outStr

    curChar = nextChar = digits[0]
    runLen = 1

    for digit in digits[1:]:
        nextChar = digit

        if nextChar == curChar:
            runLen += 1
        else:
            outStr += "%s%s" % (runLen, curChar)
            curChar = nextChar
            runLen = 1

    if nextChar == curChar:
        outStr += "%s%s" % (runLen, curChar)
    return outStr


assert "121325" == look_and_say("2355")
assert "12" == look_and_say("2")
assert "12431443" == look_and_say("2333343333")
assert "" == look_and_say("")
assert "32" == look_and_say("222")
assert "10" == look_and_say("0")
assert "121314121314252719" == look_and_say("23423455779")

Also can you make this private?