[Algorithm] How many meeting rooms needed?

Give you set of meetings start time and end time, count how many meeting rooms needed.

For example:

[[2, 5], [1, 3], [2, 7], [6, 8]] // needs 3 meeting rooms

We can use a memo table to store the at which time how many rooms needed. It is sort of like Knapsack problem. Check out this post for similar question.

Code:

function* generateAry(start, end) {
  let i = start;
  while (i <= end) {
    yield i;
    i++;
  }
}

// O(N*K): K: number of hours, N: number of room
// S(K)
function availableRoom(arys) {const { min, max } = arys.reduce(
    (acc, ary) => {
      const [start, end] = ary;
      let { min, max } = acc;
      if (start < min) {
        min = start;
      }
      if (end > max) {
        max = end;
      }
      return { min, max };
    },
    { min: Infinity, max: 0 }
  );
  const hours = Array.from(generateAry(min, max));
  const memo = hours.map(x => 0);

  function helper(arys, hours, memo) {
    let countRooms = 0;

    for (let row in arys) {
      for (let col in hours) {
        let prevCount = memo[col];
        let [min, max] = arys[row];
        // if the min > hour, set previous row same col value, the same as max < hour
        if (min > hours[col] || max < hours[col]) {
          memo[col] = prevCount;
          continue;
        }

        if (min <= hours[col] && max >= hours[col]) {
          memo[col] = prevCount + 1;
        }

        countRooms = Math.max(countRooms, memo[col]);
      }
    }
    console.log(memo); // [1, 3, 3, 2, 2, 2, 2, 1]
    return countRooms;
  }

  return helper(arys, hours, memo);
}

console.log(availableRoom([[2, 5], [1, 3], [2, 7], [6, 8]])); // 3