Python, Functional style


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    We write a function apply that takes two sets of possibilities for A and B and returns all possible results operator(A, B) or operator(B, A) for all possible operators.

    Ignoring reflection, there are only two ways we can apply the operators: (AB)(CD) or ((AB)C)D. When C and D are ordered, this becomes three ways - the third way is ((AB)D)C.

    This solution is a little slow because it has to manage sets - my article has a solution that is almost 10x faster. I think this one is cool though.

    def judgePoint24(self, nums):
        from operator import truediv, mul, add, sub
        from fractions import Fraction
    
        def apply(A, B):
            ans = set()
            for x, y, op in itertools.product(A, B, (truediv, mul, add, sub)):
                if op is not truediv or y: ans.add(op(x, y))
                if op is not truediv or x: ans.add(op(y, x))
            return ans
        
        A = [{x} for x in map(Fraction, nums)]
        for i, j in itertools.combinations(range(4), 2):
            r1 = apply(A[i], A[j])
            k, l = {0, 1, 2, 3} - {i, j}
            if 24 in apply(apply(r1, A[k]), A[l]): return True
            if 24 in apply(apply(r1, A[l]), A[k]): return True
            if 24 in apply(r1, apply(A[k], A[l])): return True
        
        return False
    

  • 0
    B

    @awice said in Python, Functional style: You said my article has a solution that is almost 10x faster - where can I find your article?


  • 0

  • 0
    B

    @awice Thank you. :)


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