Imperative code in functional languages is fun

gistfile1.fs

let d = 4

let a = Array.create (d*d) 0
let results = System.Collections.Generic.Dictionary<int,int>()

for n=0 to (1<<<d*d)-1 do
  // make a new a
  for i=0 to d*d-1 do
    if ((n &&& (1<<<i)) <> 0) then
      a.[i] <- 1
    else
      a.[i] <- 0

  // count greens
  let mutable greens = 0
  for y=0 to d-1 do
    for x=0 to d-1 do
      let mutable neighbors = 0
      if x>0   && a.[(x-1)+y*d]=1 then neighbors <- neighbors + 1
      if x<d-1 && a.[(x+1)+y*d]=1 then neighbors <- neighbors + 1
      if y>0   && a.[x+(y-1)*d]=1 then neighbors <- neighbors + 1
      if y<d-1 && a.[x+(y+1)*d]=1 then neighbors <- neighbors + 1
      if (neighbors%2)=0 then greens <- greens + 1

  if results.ContainsKey greens then
    results.[greens] <- (results.[greens]+1)
  else
    results.Add( greens, 1 )

// print results
let keys = Array.sort (Array.ofSeq results.Keys)
for key in keys do
  printfn "%O: %O" key results.[key]

// 0: 16
// 2: 256
// 3: 512
// 4: 1472
// 5: 4608
// 6: 7936
// 7: 11264
// 8: 13408
// 9: 11264
// 10: 7936
// 11: 4608
// 12: 1472
// 13: 512
// 14: 256
// 16: 16