--description--

Given a 4x2 matrix (array of arrays) representing the seating arrangement for a meal, determine how many seats a left-handed person can sit at.

• A left-handed person cannot sit where a right-handed person would be in the seat to the immediate left of them.

In the given matrix:

• An "R" is a seat occupied by a right-handed person.
• An "L" is a seat occupied by a left-handed person.
• A "U" is an unoccupied seat.
• Only unoccupied seats are available to sit at.
• The seats in the top row are facing "down", and the seats in the bottom row are facing "up" (like a table), so left and right are relative to the seat's orientation.
• Corner seats only have one seat next to them.

For example, in the given matrix:

[
  ["U", "R", "U", "L"],
  ["U", "R", "R", "R"]
]

The top-left seat is cannot be sat in because there's a right-handed person to the left. The other two open seats can be sat in because there isn't a right-handed person to the left.

--hints--

findLeftHandedSeats([["U", "R", "U", "L"], ["U", "R", "R", "R"]]) should return 2.

assert.equal(findLeftHandedSeats([["U", "R", "U", "L"], ["U", "R", "R", "R"]]), 2);

findLeftHandedSeats([["U", "U", "U", "U"], ["U", "U", "U", "U"]]) should return 8.

assert.equal(findLeftHandedSeats([["U", "U", "U", "U"], ["U", "U", "U", "U"]]), 8);

findLeftHandedSeats([["U", "R", "U", "R"], ["L", "R", "R", "U"]]) should return 0.

assert.equal(findLeftHandedSeats([["U", "R", "U", "R"], ["L", "R", "R", "U"]]), 0);

findLeftHandedSeats([["L", "U", "R", "R"], ["L", "U", "R", "R"]]) should return 1.

assert.equal(findLeftHandedSeats([["L", "U", "R", "R"], ["L", "U", "R", "R"]]), 1);

findLeftHandedSeats([["U", "R", "U", "U"], ["U", "U", "L", "U"]]) should return 5.

assert.equal(findLeftHandedSeats([["U", "R", "U", "U"], ["U", "U", "L", "U"]]), 5);

--seed--

--seed-contents--

function findLeftHandedSeats(table) {

  return table;
}

--solutions--

function findLeftHandedSeats(table) {
  let availableSeats = 0;

  const [topRow, bottomRow] = table;

  for (let i=0; i<topRow.length; i++) {
    if (topRow[i] === 'U') {
      if (i === 3) {
        availableSeats++;
      } else if (topRow[i+1] !== 'R') {
        availableSeats++;
      }
    }
  }

  for (let i=0; i<bottomRow.length; i++) {
    if (bottomRow[i] === 'U') {
      if (i === 0) {
        availableSeats++;
      } else if (bottomRow[i-1] !== 'R') {
        availableSeats++;
      }
    }
  }

  return availableSeats;
}