First uncategorized solution for How Much Gold by bunnychai - python coding challenges

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First solution in Uncategorized category for How Much Gold by bunnychai

# migrated from python 2.7
def checkio(alloys):
    """
        Find proportion of gold, assume exist unique solution.
    """
    return 1 - sum([1 - v if 'gold' in k else v for (k, v) in alloys.items()]) / 2

Sept. 29, 2013

Comments:

bunnychai on Sept. 29, 2013, 5:06 a.m.
because the matrix is special, so as the inverse, so no need to find inverse or do elimination explicitly...

Amachua on Sept. 30, 2013, 7:56 a.m.
Haha... So I didn't have to compute the inverse matrix... Nice solution :)

scturtle on Sept. 29, 2013, 1:32 p.m.
Aha!

Kush82 on Oct. 2, 2013, 6:48 a.m.
Very smart solution! But it works only if all alloys of two components. However in task: <blockquote> composed of metal names separated by a dash (Ex: "gold-tin", "iron-copper", "iron-gold-tin") </blockquote> Unfortunatly tests dont cover this case.

bryukh on Oct. 2, 2013, 10:49 a.m.
Nice

veky on Oct. 13, 2013, 5:44 a.m.
Bravo, bravo, bravo! Again, tests don't test, and bunny scores! :-D

nickie on Dec. 15, 2013, 6:53 p.m.
This is a great solution because the story says: "alloy names are presented as strings, which are composed of two metal names". If there were more elements in an alloy, you'd need a more generic method to solve a linear system of equations. Well done.

nickie on Dec. 15, 2013, 10:01 p.m.
On the other hand, how about this? <pre class='brush: python'>assert checkio({ 'gold-tin': Fraction(1, 2), 'gold-iron': Fraction(1, 3), 'gold-copper': Fraction(1, 4), 'iron-gold': Fraction(1, 3), }) == Fraction(1, 24), "kill the bunny!" </pre> It seems that the solution is based on the fact that, for the test case to be solvable, there have to be exactly three equations, which can be converted to three equations giving the values of "gold+iron", "gold+copper" and "gold+tin". This is not the case if you have duplicated equations (you need to reverse the order, or the dictionary does not allow duplicates).

bunnychai on Dec. 16, 2013, 2:53 a.m.
ya, it does not work for over-determined systems, only work for system of 3 equations which gives a unique solution...

shreekar on Dec. 26, 2013, 11:37 a.m.
I got the main logic right, but your final solution is much simpler and easier than mine.

wiking on March 10, 2014, 4:48 a.m.
Wow, awesome!

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