# Before I begin, this challenge was not mine originally

Credits to The University of Waterloo. This came from the Canadian Computing Competition 2016, Senior Problem 5. Here is a clickable link to the contest PDF:

http://cemc.uwaterloo.ca/contests/computing/2016/stage%201/seniorEn.pdf

Here is a link to the site:

http://cemc.uwaterloo.ca/contests/past_contests.html

# Challenge

Given a wrapping array of two constant values, determine the configuration after n evolutions for positive integer input n. These two values represent a living cell and a dead cell. Evolutions work like this:

# Evolution!

After each iteration, a cell is alive if it had exactly one living neighbor in the previous iteration. Any less and it dies of loneliness; any more and it dies of overcrowding. The neighbourhood is exclusive: i.e. each cell has two neighbours, not three.

For example, let's see how 1001011010 would evolve, where 1 is a living cell and 0 is a dead cell.

(0) 1 0 0 1 0 1 1 0 1 0 (1)
*   $%  The cell at the * has a dead cell on both sides of it so it dies of lonliness. The cell at the $ has a living cell on one side of it and a dead cell on the other. It becomes alive.
The cel at the % has a living cell on both sides of it so it stays dead from overcrowding.

# Winning Criteria

Shortest code wins.

# I/O

Input will be a list of the cell states as two consistent values, and an integer representing the number of inputs, in some reasonable format. Output is to be a list of the cell states after the specified number of iterations.

# Test Cases

start, iterations -> end
1001011010, 1000 -> 1100001100
100101011010000, 100 -> 000110101001010
0000000101011000010000010010001111110100110100000100011111111100111101011010100010110000100111111010, 1000 -> 1001111111100010010100000100100100111010010110001011001101010111011011011100110110100000100011011001

• I don't think this should be tagged as code golf if byte count is merely a tiebreaker. I'm also not sure if it is a good tiebreaker, as the contest will degenerate to a code golf competition if you can simply port answers to a more concise language to win. May 30, 2017 at 3:10
• @Dennis Right, I will remove the tag. What do you suggest for tiebreaking then; earliest submission is another one of my ideas. May 30, 2017 at 3:12
• I'm voting as unclear for the moment since it's unknowable what is meant by complexity when there are multiple parameters. May 30, 2017 at 3:43
• @feersum, there is a tiny bit of play in fastest-algorithm. The naïve algorithm takes Theta(nt) where n is the length of the array and t is the number of evolutions; a faster algorithm takes Theta(n lg t). May 30, 2017 at 7:23
• @Notts90 I hope my latest edit clarifies it more. May 30, 2017 at 12:56

# APL (Dyalog),14 bytes

Prompts for start state as Boolean list and then for number of iterations

(1∘⌽≠¯1∘⌽)⍣⎕⊢⎕


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⎕ numeric prompt (for Boolean list of start state)

⊢ on that, apply

()⍣⎕ the following tacit function, numeric-prompt times

¯1∘⌽ the argument rotated one step right

≠ different from (XOR)

1∘⌽ the argument rotated one step left

# Jelly, 7 bytes

ṙ2^ṙ-µ¡


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Explanation

ṙ2^ṙ-µ¡
µ¡  - repeat a number of times equal to input 2:
ṙ2         - previous iteration rotated 2 to the left
^        - XOR-ed with:
- (implicit) previous iteration
ṙ-      - rotate back (by negative 1 to the left)


# 05AB1E, 6 bytes

FDÀÀ^Á


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Explanation

F        # input_1 times do
D       # duplicate last iteration (input_2 the first iteration)
ÀÀ     # rotate left twice
^    # XOR
Á   # rotate right