day_21.nfo

// Advent of Code 2017
// Day 21

Notes:
* no way for 2rules not to match

rules
2x2 -> 3x3
3x3 -> 4x4

hash all rule inputs for 2x2 and 3x3
flip x, flip y, rot 90, rot 180, rot 270

hash2x2 [0,1,2,3]
    for i=0 .. 3 hash|=(bit[i]<<i)

[[0,1,2,3],[2,3,0,1],[1,0,3,2],[1,3,0,2],[3,2,0,1],[2,0,3,1]]
hash2x2mult input output =
    for each configuration
        for i=0 .. 3 hash|=(bit[i]<<i)


split2:
    for r=0 .. side/2-1
        for c=0 ... side/2-1
            hash = 


Structures:

2rules: hash -> output 3x3
3rules: hash -> output 4x4

bitmap
    split2 -> list hashes
    split3 -> list hashes
    unify list hashes -> bitmap

unify: list outputs
    create a new bitmap -> vector<bool> bitmap
    for each list output
        copy output into bitmap

Read rules
Hash rule matches and create 2map hash -> output and 3map hash -> output

bitmap <- input
While not done count
    split2 or split3 bitmap to list of hashes (by row the col)
    [match hashes to output rules]
    generate2x2 or generate3x3 from list of hashes
    unify list of hashes