SRM620 Div1 Easy なんかアリーナだとエラー出る。謎。

PairGame.py

class PairGame:
    def maxSum(self, a, b, c, d):
        partA = self.parts(a, b)
        partC = self.parts(c, d)
        group = sorted(list(partA.items()), reverse=True)
        for g in group:
            if partC.has_key(g[0]):
                if partC[g[0]] == g[1]:
                    return g[0]
        return -1

    def parts(self, a, b):
        dict = {}
        dict[a + b] = (a, b)
        while a > 0 and b > 0:
            if a > b:
                a, b = a - b, b
            else:
                a, b = a, b - a
            dict[a + b] = (a, b)
        return dict