const X = 1;

const O = -1;

const TIE = 0;

var board;

var turn;

var finished;

var buffer;

var w;

​

let round = 0;

​

function setup() {

  createCanvas(600, 700);

  textSize(30);

  w = width / 3;

  buffer = w / 4;

  finished = false;

  turn = X;

  //draw board

  fill(255);

  for (let i = 0; i < 3; i++) {

    for (let j = 0; j < 3; j++) {

      strokeWeight(1);

      rect(i * w, j * w, w, w);

    }

  }

  board = [

    [VOID, VOID, VOID],

    [VOID, VOID, VOID],

    [VOID, VOID, VOID]

  ];

​

  fill(255);

  strokeWeight(1);

  rect(0, 3 * w, 3 * w, w / 2);

  if(round%2==0) {

    let next = findBestTurn(board, turn, 0);

    turn = makeTurn(board, next.x, next.y, turn);

  }

}

​

function draw() {

  fill(255);

  strokeWeight(1);

  rect(0, 600, 600, w / 2);

​

  if (!finished) {

    if (turn == X) {

      fill(0);

      text("X ist dran", w, 3 * w + buffer);

    } else {

      fill(0);

      text("O ist dran", w, 3 * w + buffer);

    }

  }

  drawBoard(board);

  checkAndFinish(board);

​

​

}

​

function mouseReleased() {

  if (!finished) {

    var x = mouseX;

    var y = mouseY;

    noFill();

    //check board and draw corresponding shape on right field

    for (let i = 0; i < 3; i++) {

      for (let j = 0; j < 3; j++) {

        if (isbetween2(x, y, i * w, (i + 1) * w, j * w, (j + 1) * w) && board[i][j] == VOID) {

          turn = makeTurn(board, i, j, turn);

          if (checkAndFinish(board) == true) {

            return;

          }

          let next = findBestTurn(board, turn, 0);

          if (next.x != -1) {

            turn = makeTurn(board, next.x, next.y, turn);

          }

        }

      }

    }

  } else {

    finished = false;

    round++;

    setup();

  }

}

​

function makeTurn(board, x, y, player) {

  board[x][y] = player;

  return nextTurn(player);

}

​

function drawBoard(board) {

  for (let x = 0; x < board.length; x++) {

    for (let y = 0; y < board[0].length; y++) {

      let player = board[x][y];

      noFill();

      if (player == O) {

        strokeWeight(4);

        ellipse(x * w + w / 2, y * w + w / 2, w / 2, w / 2);

      } else if (player == X) {

        strokeWeight(4);

        cross(x * w + w / 2, y * w + w / 2, w - buffer);

      }

    }

  }

}

​

function nextTurn(turn) {

  if (turn == O) {

    return X;

  }

  return O;

}

​

function findBestTurn(b, player, count) { //find best Turn for player wiht minimax

  let board = copyArray(b);

  let max = player == X;

  let best = {

    x: -1,

    y: -1,

    sc: 2

  };

  if (max) {

    best.sc = -2;

  }

​

  for (let i = 0; i < board.length; i++) {

    for (let j = 0; j < board[0].length; j++) {

      if (board[i][j] == VOID) { //if no occupied => make that turn and score it

        board[i][j] = player;

        let curr = {

          x: i,

          y: j,

          sc: score(board, player, count) //score of the turn 1: X wins, -1: O wins, 0: tie

        };

        if (max) { //if solving for best turn for X: we want maximum turn (so that X wins)

          if (curr.sc > best.sc) {

            best = curr;

          }

        } else { //if solving for best turn for O: we want minimum turn (so that O wins)

          if (curr.sc < best.sc) {

            best = curr;

          }

        }

        board[i][j] = VOID;

      }

    }

  }

​

  return best;

​

​

}

​

function score(board, player, count) {

  let winner = checkWinner(board, false);

  if (winner != VOID) {

    return winner;

  }

  let next = findBestTurn(board, nextTurn(player), count + 1);

  return next.sc;

}

​

​

​

function checkWinner(board, draw) {

  //horizontal

  for (let j = 0; j < 3; j++) {

    if (areequal(board[0][j], board[1][j], board[2][j]) && board[0][j] != VOID) {

      if (draw) {

        strokeWeight(16);

        line(buffer, j * w + w / 2, 3 * w - buffer, j * w + w / 2);

      }

      return board[0][j];

    }

  }

  //vertical

  for (let i = 0; i < 3; i++) {

    if (areequal(board[i][0], board[i][1], board[i][2]) && board[i][0] != VOID) {

      if (draw) {

        strokeWeight(16);

        line(i * w + w / 2, buffer, i * w + w / 2, 3 * w - buffer);

      }

      return board[i][0];

    }

  }

  //diagonals

  if (areequal(board[0][0], board[1][1], board[2][2]) && board[0][0] != VOID) {

    if (draw) {

      strokeWeight(16);

      line(buffer, buffer, 3 * w - buffer, 3 * w - buffer);

    }

    return board[0][0];

  }

  if (areequal(board[2][0], board[1][1], board[0][2]) && board[2][0] != VOID) {

    if (draw) {

      strokeWeight(16);

      line(3 * w - buffer, buffer, buffer, 3 * w - buffer);

    }

    return board[2][0];

  }

​

  //go through every field and return no winner (VOID) if at least one field is still empty

  for (let i = 0; i < 3; i++) {

    for (let j = 0; j < 3; j++) {

      if (board[i][j] == VOID) {

        return VOID;

      }

    }

  }

  //else... (noone has three in a row, every field is obtained)

  return TIE;

}

​

function checkAndFinish(board) {

  let winner = checkWinner(board, true);

  if (winner != VOID) {

    finished = true;

    if (winner == X) {

      fill(0);

      text("X hat gewonnen", w, 650);

      //println(X);

    } else if (winner == O) {

      fill(0);

      text("O hat gewonnen", w, 650);

      //println(O);

    } else {

      fill(0);

      text("Unentschieden", w, 650);

      //println(TIE);

    }

  }

  return finished;

}

​

function copyArray(arr) {

  let cop = [];

​

  for (var i = 0; i < arr.length; i++) {

    cop[i] = arr[i].slice();

  }

  return cop;

}

​

​

function areequal(a, b, c) {

  return a == b && b == c;

}

//function drawing the cross

function cross(x, y, w) {

  line(x - w / 2, y - w / 2, x + w / 2, y + w / 2);

  line(x + w / 2, y - w / 2, x - w / 2, y + w / 2);

}

​

function isbetween(x, a, b) {

  return x >= a && x <= b;

}

​

function isbetween2(x, y, a, b, c, d) {

  return isbetween(x, a, b) && isbetween(y, c, d);

}