Euler Problem 92

28 Sep 2013 - Lorentz Vedeler

Here’s my solution to Euler problem 92. The code is pretty simple, it tries to shortcut the sequence by storing every number in a chain along with the number that recurs.

class Euler92:
    def __init__(self):
        self.knownSeq = {}

    def ChainNumber(self,n):
        currentSeq = []
        while not n in [1,89]:
            currentSeq.append(n)
            if(n in self.knownSeq):
                n = self.knownSeq[n]
            else:
                n = SquareDigits(n)
        for x in currentSeq:
            self.knownSeq[x] = n
        return n

    def Solve(self, n):
        return len([x for x in range(2,n) if self.ChainNumber(x) == 89])
        
def SquareDigits(n):
        return sum(map(lambda x: int(x)**2, str(n)))