Functional DP creative solution for Golden Pyramid by nickie - python coding challenges

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Functional DP solution in Creative category for Golden Pyramid by nickie

count_gold=lambda p:__import__("functools").reduce(lambda D,r:[x+max(D[j],D[j+1])
for j,x in enumerate(r)],p[-2::-1],list(p[-1]))[0]

April 30, 2014

Comments:

veky on May 8, 2014, 6:26 a.m.
Yes. :-) But why do you listify p[-1] at the end?

nickie on May 8, 2014, 6:42 a.m.
I think reduce will return the initializer immediately if p[-2::-1] is empty, i.e., if the pyramid is of height 1. Listifying is redundant if you don't mind the result being a tuple instead of a list, in that case. It certainly passes the test cases. But I come from a typed functional world... :-)

veky on May 8, 2014, 6:55 a.m.
That is what bothers me. The only reason you might care about whether it is a list or a tuple is if you intend to modify it, and that's something a hardcore functional fanatic would never do. :-D Also, unrelated, you can give a slice D[j:j+2] to max.

nickie on May 8, 2014, 7:26 a.m.
It's not a matter of modification, after all the result of reduce (list or tuple) is never modified, only accessed once. It's a matter of type-checking (which of course is irrelevant to Python): my strongly-typed and limited brain saw tuples and lists as different things and was compelled to fix that.

veky on May 8, 2014, 7:48 a.m.
Ah, now I get it. It bothered you that in one case, you [0] with list.__getitem__, and in another with tuple.__getitem__. Of course, in any decent functional programming language, tuple and list would be the same type. :-) Interesting question: if I remember correctly, in your fantastic "Median" solution (linear selection algorithm), you did return int if list had odd number of elements, but float if it had even. There it didn't bother you? :-)

nickie on May 8, 2014, 9:04 a.m.
Can't let anything fall, eh? You're right. :-) But it was the task description that forced me to return a float (the result type of /, to be precise) for lists of even length, and a list element (whatever its type may have been, int or float or any other comparable type) for lists of odd length. In a strongly typed language, this task description would have been problematic.

veky on May 8, 2014, 9:12 a.m.
<blockquote> Can't let anything fall, eh? </blockquote> Just my elephantine memory. Trust me, it's more often a curse than a blessing. :-D (But yes, when you can keep whole Django documentation in your head, it has certain advantages.;)

Look up in the Dict()

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