RunCustomerSimulation.js

/**
 * @author Anirudh Sharma
 * 
 * Write a function "runCustomerSimulation" that takes following two inputs
 * a) An integer 'n': total number of computers in a cafe and a string:
 * b) A sequence of uppercase letters ‘seq’: Letters in the sequence occur in pairs.
 * The first occurrence indicates the arrival of a customer;
 * the second indicates the departure of that same customer.
 * 
 * A customer will be serviced if there is an unoccupied computer.
 * No letter will occur more than two times.
 * 
 * Customers who leave without using a computer always depart before customers who are
 * currently using the computers. There are at most 20 computers per cafe.
 * 
 * For each set of input the function should output a number telling how many customers,
 * if any walked away without using a computer.
 * 
 * Return 0 if all the customers were able to use a computer.
 */
const runSimulation = (n, sequence) => {
    // Array to represents the states of a customer
    // customerStates[i] = 0 => customer i is not in cafe
    // customerStates[i] = 1 > customer i is in but with no computer
    // customerStates[i] = 2 => customer i is in cafe with computer
    const customerStates = Array(26).fill(0);
    // Number of customers who won't get a computer
    let customerCount = 0;
    // Track of occupied computers
    let occupiedComputerCount = 0;
    // Loop through the sequence
    for (let c of sequence) {
        // Index of the current character
        let index = c.charCodeAt(0) - 'A'.charCodeAt(0);
        // If the customer is first time in the cafe
        if (customerStates[index] === 0) {
            // Change its state
            customerStates[index] = 1;
            // If the computer can be occupied
            if (occupiedComputerCount < n) {
                // Give the computer to the customer
                customerStates[index] = 2;
                occupiedComputerCount++;
            } else {
                // Since the computer can't be assigned
                customerCount++;
            }
        }
        // If the customer is already in the cafe
        else {
            if (customerStates[index] === 2) {
                occupiedComputerCount--;
            }
            customerStates[index] = 0;
        }
    }
    return customerCount;
};

const main = () => {
    console.log(runSimulation(2, "ABBAJJKZKZ".split('')));
    console.log(runSimulation(3, "GACCBDDBAGEE".split('')));
    console.log(runSimulation(3, "GACCBGDDBAEE".split('')));
    console.log(runSimulation(1, "ABCBCA".split('')));
    console.log(runSimulation(1, "ABCBCADEED".split('')));
};

main();