'''
   primechecker.py
   Jeff Ondich, 9 May 2012

   A small sample class to be tested by unittest-based test cases. See
   primetests.py for the rest of this sample.
'''

class PrimeChecker:
    def __init__(self, maxInteger):
        self.maxInteger = 0
        self.initializeSieve(maxInteger)

    def initializeSieve(self, maxInteger):
        ''' Initializes a Sieve of Eratothsenes up to but not including maxInteger.
            Precondition: maxInteger is an integer greater than 1. '''
        assert type(maxInteger) == type(0)
        assert maxInteger > 1
        if maxInteger > self.maxInteger:
            self.maxInteger = maxInteger
            self.sieve = [0] * self.maxInteger
            self.sieve[0] = 1
            self.sieve[1] = 1
            currentPrime = 2
            while currentPrime < self.maxInteger:
                k = currentPrime * 2
                while k < self.maxInteger:
                    self.sieve[k] = 1
                    k += currentPrime
                currentPrime += 1
                while currentPrime < self.maxInteger and self.sieve[currentPrime] == 1:
                    currentPrime += 1

    def getPrimesBelow(self, n):
        ''' Returns the list of primes strictly less than n, sorted in increasing order. '''
        self.initializeSieve(n)
        primes = [k for k in range(n) if self.sieve[k] == 0]
        return primes

    def isPrime(self, n):
        if type(n) != type(0) or n < 2:
            return False

        self.initializeSieve(n + 1)
        return self.sieve[n] == 0