Solution to http://www.codewars.com/kata/tic-tac-toe-checker/train/javascript

tic_tac_toe_solver.js

function isSolved(board) {
  const getWins = makeGetWins(board)
  return getWins(1) ? 1 : getWins(2) ? 2 :  emptySlots(board) ? -1 : 0
}

const makeGetWins = board => key => 
  [
    horizontalWin(board, key),
    verticalWin(board, key),
    leftDiagWin(board, key),
    rightDiagWin(board, key)
  ].some(_=>Boolean(_))
  
const emptySlots = board =>
  board.map(x=>x.some(_=>_===0)).some(_=>Boolean(_))
  
const horizontalWin = (board, key) =>
  board.map(x => x.every(_=>_===key)).some(_=>Boolean(_))

const verticalWin = (board, key) =>
  horizontalWin(rotateBoard(board), key)
  
const leftDiagWin = (board, key) =>
  [0,1,2].map((winIdx, rowIdx) => board[rowIdx][winIdx] === key).every(_=>Boolean(_)) 

const rightDiagWin = (board, key) =>
  [2,1,0].map((winIdx, rowIdx) => board[rowIdx][winIdx] === key).every(_=>Boolean(_)) 
  
const rotateBoard = board => 
  Array(board[0].length)
    .fill(null)
    .map((x,idx) => board.map(_ => _[idx])) 

If we were to set up a Tic-Tac-Toe game, we would want to know whether the board's current state is solved, wouldn't we? Our goal is to create a function that will check that for us!

Assume that the board comes in the form of a 3x3 array, where the value is 0 if a spot is empty, 1 if it is an "X", or 2 if it is an "O", like so:

[[0, 0, 1],
[0, 1, 2],
[2, 1, 0]]
We want our function to return:

-1 if the board is not yet finished (there are empty spots),
1 if "X" won,
2 if "O" won,
0 if it's a cat's game (i.e. a draw).
You may assume that the board passed in is valid in the context of a game of Tic-Tac-Toe.