tictactoev1

const readline = require("readline").createInterface({
  input: process.stdin,
  output: process.stdout
})

let PLAYER = "X"
let CPU = "O"

// cpu is with max

const decr = x => x - 1

const parseWinner = w => {
  if (w === PLAYER) {
    return "PLAYER wins"
  }

  if (w === CPU) {
    return "CPU wins"
  }

  return "Tie."
}

const generateBoard = () => {
  const brd = []
  for (let i = 0; i < 3; i++) {
    brd.push(Array.from({ length: 3 }, () => "_"))
  }
  return brd
}

const printBoard = board => {
  board.forEach(row => {
    console.log(row.join(" "))
  })
  console.log()
}

const isValid = (board, row, col) =>
  0 <= row && row <= 2 && 0 <= col && col <= 2 && board[row][col] === "_"

const getWinner = board => {
  for (let i = 0; i < 3; i++) {
    if (
      board[0][i] !== "_" &&
      board[0][i] === board[1][i] &&
      board[1][i] === board[2][i]
    ) {
      return board[0][i]
    }
  }

  for (let i = 0; i < 3; i++) {
    if (
      board[i][0] !== "_" &&
      board[i][0] === board[i][1] &&
      board[i][1] === board[i][2]
    ) {
      return board[i][0]
    }
  }

  if (
    board[0][0] !== "_" &&
    board[0][0] === board[1][1] &&
    board[1][1] === board[2][2]
  ) {
    return board[0][0]
  }

  if (
    board[0][2] !== "_" &&
    board[0][2] === board[1][1] &&
    board[1][1] === board[2][0]
  ) {
    return board[0][2]
  }

  // _ if tie, undefined if still no winner
  return board.every(row => row.every(el => el !== "_")) ? "_" : undefined
}

function min(board, level = 0, alphaIn = -Infinity, betaIn = Infinity) {
  let minValue = Infinity
  let minRow = undefined
  let minCol = undefined

  let alpha = alphaIn
  let beta = betaIn

  const winner = getWinner(board)
  if (winner === PLAYER) {
    return [-1 * (10 - level)]
  }
  if (winner === CPU) {
    return [1 * (10 - level)]
  }
  if (winner === "_") {
    return [0]
  }

  for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 3; j++) {
      if (board[i][j] === "_") {
        board[i][j] = PLAYER
        let [maxValue] = max(board, level + 1, alpha, beta)
        if (maxValue < minValue) {
          minValue = maxValue
          minRow = i
          minCol = j
        }
        board[i][j] = "_"

        if (minValue <= alpha) {
          return [minValue, minRow, minCol]
        }

        if (minValue < beta) {
          beta = minValue
        }
      }
    }
  }

  return [minValue, minRow, minCol]
}

function max(board, level = 0, alphaIn = -Infinity, betaIn = Infinity) {
  let maxValue = -Infinity
  let maxRow = undefined
  let maxCol = undefined

  let alpha = alphaIn
  let beta = betaIn

  const winner = getWinner(board)
  if (winner === PLAYER) {
    return [-1 * (10 - level)]
  }
  if (winner === CPU) {
    return [1 * (10 - level)]
  }
  if (winner === "_") {
    return [0]
  }

  for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 3; j++) {
      if (board[i][j] === "_") {
        board[i][j] = CPU
        let [minValue] = min(board, level + 1, alpha, beta)
        if (minValue > maxValue) {
          maxValue = minValue
          maxRow = i
          maxCol = j
        }
        board[i][j] = "_"

        if (maxValue >= beta) {
          return [maxValue, maxRow, maxCol]
        }

        if (maxValue > alpha) {
          alpha = maxValue
        }
      }
    }
  }

  return [maxValue, maxRow, maxCol]
}

// main
const board = generateBoard()
printBoard(board)

let linesRead = 0
let firstPlayer = "PLAYER"

readline.on("line", line => {
  if (linesRead++ === 0) {
    firstPlayer = line
    if (firstPlayer === "CPU") {
      CPU = "X"
      PLAYER = "O"
    } else {
      const [_, i, j] = min(board)
      console.log(`The algorithm suggests you pick ${i + 1} ${j + 1}`)
      return
    }
  }

  // player
  if (linesRead > 1 || firstPlayer !== "CPU") {
    const [row, col] = line
      .split(" ")
      .map(Number)
      .map(decr)

    const valid = isValid(board, row, col)
    if (!valid) {
      console.log("Invalid move, try again.")
      return
    }

    board[row][col] = PLAYER
    printBoard(board)
  }

  const winner = getWinner(board)
  if (winner) {
    console.log(parseWinner(winner))
    readline.close()
    return
  } else {
    // CPU
    const [_, i, j] = max(board)
    board[i][j] = CPU
    printBoard(board)

    const winnerAfterCpu = getWinner(board)
    if (winnerAfterCpu) {
      console.log(parseWinner(winnerAfterCpu))
      readline.close()
      return
    }
  }

  const [_, i, j] = min(board)
  console.log(`The algorithm suggests you pick ${i + 1} ${j + 1}`)
})