Advent of code 2019 day 4

day4a.py

#! python
# https://adventofcode.com/2019/day/4

min = 265275
max = 781584
counter = 0


def check_pw(n):
    """
    dupe: number has at least one pair of equal adjacent digits
    Will return true if the number has at least one pair of
    adjacent digits and the digits never decrease.
    """
    dupe = False
    prev = None
    for c in str(n):
        if prev is not None:
            if c == prev:
                dupe = True
            elif c < prev:
                return False
        prev = c
    # if we got here, no decreasing digits
    return dupe


for p in range(min, max + 1):
    if check_pw(p):
        counter += 1

print(counter)

day4b.py

#! python
# https://adventofcode.com/2019/day/4

min = 265275
max = 781584
counter = 0


def check_pw(n):
    """
    Will return true if the number has at least one pair of
    adjacent digits that are not part of a larger set of
    adjacent digits, and the digits never decrease.
    So now we need to keep track of how many repeats
    there are in a repeating group, and add to the count
    only if there is exactly 1 repeat (i.e.: a pair).
    We return true if there are no descending digits
    and there is at least one pair.
    """
    pairs = 0
    repeats = 0
    prev = None
    for c in str(n):
        if prev is not None:
            if c < prev:
                # ooops, decreased
                return False
            elif c == prev:
                # a possible pair
                repeats += 1
            else:
                # different and larger
                if repeats == 1:
                    # found a pair!
                    pairs += 1
                repeats = 0 # reset
        prev = c
    # if we got here, no decreasing digits
    # were the last 2 digits a pair?
    if repeats == 1:
        pairs += 1
    return (pairs > 0)


for n in [ 112233, 123444, 111122 ]:
    print( "{} -> {}".format(n, check_pw(n)))


for p in range(min, max + 1):
    if check_pw(p):
        counter += 1

print(counter)