count number of possible positions after three moves in the game of go

gopositions.nim

import std/sequtils
import std/strutils
import std/tables

type board = array[1..19, array[1..19, char]]

var table = initTable[string, int]()
var count:int = 0

proc print(a:board) =
  for i in 1..19:
    for j in 1..19:
      stdout.write a[i][j]
    echo ""
  echo ""

proc rotate(a: board) : board =
  var r: board
  for i in 1..19:
    for j in 1..19:
      r[i][j] = a[j][20-i]
  return r

proc revert(a: board) : board =
  var r: board
  for i in 1..19:
    for j in 1..19:
      r[i][j] = a[i][20-j]
  return r

proc to_string(a:board) :string = a.mapIt(it.join("")).join("")

proc to_string_dic(a:board) :string =
  var tmp:board = a
  var s:string
  var r:string = to_string(tmp)
  tmp = rotate(tmp)
  for i in 1..3:
    s = to_string(tmp)
    if s > r : r = s
    tmp = rotate(tmp)
  tmp = revert(tmp)
  for i in 1..4:
    s = to_string(tmp)
    if s > r : r = s
    tmp = rotate(tmp)
  return r

proc solve(x: var board, m: int, n: int) =
  if n == m:
    var s = to_string_dic(x)
    if not table.haskey(s):
      print(x)
      table[s] = 1
      count += 1
      echo count
  else:
    var c: char
    if n mod 2 == 0: c = 'O'
    else: c = 'X'
    for i in 1..19:
      for j in 1..19:
        if x[i][j] != '.' : continue
        x[i][j] = c
        solve(x, m, n+1)
        x[i][j] = '.'

var x: board
for i in 1..19:
  for j in 1..19:
    x[i][j] = '.'
solve(x, 3, 0)
echo table.len