greplin.py

"""
Code for solving the Greplin Challenge
http://challenge.greplin.com/
"""

from itertools import chain, combinations

# Level one
def palindrome(s):
    """Find the largest palindrome in the given string."""
    slen = len(s)
    chunks = (s[i:j] for i, c in enumerate(s) for j in xrange(i, slen))
    matches = (a for a in chunks if a == a[::-1])
    return max(matches, key=len)


# Level two
def fibs():
    a, b = 0, 1
    while True:
        a, b = b, a + b
        yield b

def isprime(n):
    for x in xrange(2, int(n ** 0.5) + 1):
        if n % x == 0:
            return False
    return True

def bigprimefib(n):
    """Find the first prime number larger than n in the Fibonacci sequence."""
    for x in fibs():
        if x > n and isprime(x):
            return x

# (Plus I got the divisors of n+1 from Wolfram Alpha)


# Level three
def subsets(xs):
    """Generate a list of subsets of the given list where the largest number
    in the subset is the sum of the remaining numbers."""
    pool = chain(*[combinations(xs, i) for i in xrange(3, len(xs))])
    return [ps for ps in pool if sum(ps[:-1]) == ps[-1]]