Discussion on: Coding Puzzles: Week of 4/8

[russ]

What is this necromancy?

[Laurie]

Haha, bitwise xor. Since it's immutable and commutative it'll reduce down to the stray!

I should add that this only works because it’s an odd number of elements in the array. An even number of matching elements cancel each other out to result in the “stray”.

[russ]

Oh my, it even works in python!

def stray(arr):
    count = {}
    for index, i in enumerate(arr):
        count[i] = count.setdefault(i, 0) + 1
        if index >= 2 and len(count.keys()) > 1:
            break
    return next(k for k, v in count.items() if v == 1)

from functools import reduce

def intstray(arr: [int]):
    return reduce(lambda x,y: x ^ y, arr)

assert(intstray([1, 1, 2]) == 2)
#nope..!
#assert(intstray([1, 1, 2, 1]) == 2)
assert(intstray([17, 17, 3, 17, 17, 17, 17]) == 3)
assert(intstray([1, 2, 2]) == 1)
assert(stray(["bob", "bob", "bob", "steve", "bob"]) == "steve")

[Laurie]

This is one of those moments when I wish gifs worked better on Dev. But yay!

[Ali Spittel]

They should work in normal image markdown!

[Laurie]

Whaaa?! How did I not know this! ...game changer