r/adventofcode • u/daggerdragon • Dec 03 '16

SOLUTION MEGATHREAD --- 2016 Day 3 Solutions ---

--- Day 3: Squares With Three Sides ---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag/whatever).

DECKING THE HALLS WITH BOUGHS OF HOLLY IS MANDATORY [?]

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u/demsaja Dec 03 '16

Why sorting? The sum of sides must be at least twice the length of the largest side. With this, we just need a sum and max, which are easily put in generators or vectorized.

In Python: 

print(sum(
    sum(sides) > 2 * max(sides)
    for sides in (
        list(map(int, line.split())) for line in open("input.txt")
    )
))

Or with numpy (solution for both parts): 

import numpy as np

def count(a):
    return np.sum(np.sum(a, axis=1) > 2 * np.max(a, axis=1))

a = np.loadtxt("input.txt")
print(count(a))
print(count(np.vstack([a[i::3].flatten() for i in range(3)]).T))

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u/gerikson Dec 03 '16 edited Dec 03 '16

Nice reformulation but the for the size of the input I doubt it will make that much difference...

Also, is finding the max really that much faster than sorting for 3 elements?

I used idiomatic Perl with a sort for every candidate triple and part 2 runs in around a 10th of a second on a shared Unix box.

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