Chess Knight Tour

function solveKnightTour() {
  const length = 8;
  const empty = -1;
  // Any other structure for the offsets will slow the program down considerably.
  const xOffsets = [2, 1, -1, -2, -2, -1, 1, 2];
  const yOffsets = [1, 2, 2, 1, -1, -2, -2, -1];
  const board = Array.from({ length }, _ => Array.from({ length }, __ => empty));
  board[0][0] = 1;

  /**
   * Determines whether `board[x][y]` can be filled in.
   * @param {number} x A row index.
   * @param {number} y A column index.
   * @returns {boolean}
   */
  const isSafe = (x, y) => {
    return x >= 0 && x < length && y >= 0 && y < length && board[x][y] === empty;
  };

  /**
   * Recursively fill in the board with increasing numbers representing a complete knight tour.
   * @param {number} x The row index.
   * @param {number} y the column index.
   * @param {number} cnt The move index.
   * @returns {boolean} Whether `x` and `y` eventually lead to a complete knight tour.
   */
  const solve = (x, y, cnt = 2) => {
    if (cnt > length ** 2)
      return true;

    for (let i = 0; i < length; i++) {
      const nextX = x + xOffsets[i],
        nextY = y + yOffsets[i];
      if (!isSafe(nextX, nextY))
        continue;

      board[nextX][nextY] = cnt;
      if (solve(nextX, nextY, cnt + 1))
        return true;

      board[nextX][nextY] = empty;
    }

    return false;
  };

  solve(0, 0);
  console.log(
    board.map(row => row
      .map(n => String(n).padStart(2, "0"))
      .join("—")
    )
  );
}