1386. Cinema Seat Allocation

Description

A cinema has n rows of seats, numbered from 1 to n and there are ten seats in each row, labelled from 1 to 10 as shown in the figure above.

Given the array reservedSeats containing the numbers of seats already reserved, for example, reservedSeats[i] = [3,8] means the seat located in row 3 and labelled with 8 is already reserved.

Return the maximum number of four-person groups you can assign on the cinema seats. A four-person group occupies four adjacent seats in one single row. Seats across an aisle (such as [3,3] and [3,4]) are not considered to be adjacent, but there is an exceptional case on which an aisle split a four-person group, in that case, the aisle split a four-person group in the middle, which means to have two people on each side.

 

Example 1:

Input: n = 3, reservedSeats = [[1,2],[1,3],[1,8],[2,6],[3,1],[3,10]]
Output: 4
Explanation: The figure above shows the optimal allocation for four groups, where seats mark with blue are already reserved and contiguous seats mark with orange are for one group.

Example 2:

Input: n = 2, reservedSeats = [[2,1],[1,8],[2,6]]
Output: 2

Example 3:

Input: n = 4, reservedSeats = [[4,3],[1,4],[4,6],[1,7]]
Output: 4

 

Constraints:

• 1 <= n <= 10^9
• 1 <= reservedSeats.length <= min(10*n, 10^4)
• reservedSeats[i].length == 2
• 1 <= reservedSeats[i][0] <= n
• 1 <= reservedSeats[i][1] <= 10
• All reservedSeats[i] are distinct.

 

Solutions

Solution: Hash Table

• Time complexity: O(n * 12)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {number} n
 * @param {number[][]} reservedSeats
 * @return {number}
 */
const maxNumberOfFamilies = function (n, reservedSeats) {
  const reservedMap = reservedSeats.reduce((map, [row, labelled]) => {
    const labelleds = map.get(row) ?? new Set();

    labelleds.add(labelled);
    return map.set(row, labelleds);
  }, new Map());
  const getSeats = (labelleds, check) => {
    return check.some(labelled => labelleds.has(labelled)) ? 0 : 1;
  };
  let result = 0;

  reservedMap.forEach(labelleds => {
    const seats = getSeats(labelleds, [2, 3, 4, 5]) + getSeats(labelleds, [6, 7, 8, 9]);

    result += seats ? seats : getSeats(labelleds, [4, 5, 6, 7]);
  });

  return result + (n - reservedMap.size) * 2;
};