1386. Cinema Seat Allocation

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.

class Solution {
public:
    int maxNumberOfFamilies(int n, vector<vector<int>>& reservedSeats) {
        int res = n << 1;
        const int left = 1, right = (1<<2), leftmid = left | (1<<1), rightmid = right | (1<<1);
        const int all = left | rightmid;
        unordered_map<int, short> m;
        
        for(auto& seat : reservedSeats) {
            switch (seat.back()) {
                case 2:
                case 3: m[seat.front()] |= left; break;
                case 4:
                case 5: m[seat.front()] |= leftmid; break;
                case 6:
                case 7: m[seat.front()] |= rightmid; break;
                case 8:
                case 9: m[seat.front()] |= right; break;
            }
        }

        for(auto& seat : m) {
            res -= seat.second ^ all ? 1 : 2;
        }

        return res;
    }
};