如何确定字符串是否不是数组的一部分并计算出现次数？

Question

I have a program that takes in a series of items and prices as well as the number of customers and what/how many of the items available was purchased. I was able to figure out the inputs, but I want to know how to print which items were not purchased at all for all the customers, and how many of each item was purchased.

This is what I have so far:

    public static void main(String[] args) {
        
        Scanner scan = new Scanner(System.in);

        // Integer count of number of items in the store
        int count = scan.nextInt();

        // Create an array to store names and prices of each item
        String[] itemName = new String[count];
        double[] itemPrice = new double[count];

        for (int i=0; i<count; i++) {
            // Scan name of each item and price
            itemName[i] = scan.next();
            itemPrice[i] = scan.nextDouble();
        }

        // Integer count for the number of customers
        int numCustomers = scan.nextInt();
        String[] nameF = new String[numCustomers];
        String[] nameL = new String[numCustomers];
        double[] costs = new double[numCustomers];

        for (int j=0; j<numCustomers; j++) {
            // First and last name of each customer
            nameF[j] = scan.next();
            nameL[j] = scan.next();

            //Number of items bought
            int numItems = scan.nextInt();
            String[] customerItems = new String[numItems];

            for (int k=0; k<numItems; k++) {
                // For each number of items bought, name and quantity
                int numItemBought = scan.nextInt();
                String nameOfItem = scan.next();

                for (int i=0; i<count; i++) {
                    if (nameOfItem != itemName[i]) {
                        String msg = "No one bought " + nameOfItem;
                        System.out.println(msg);
                    }
                }
            }
        }

    }

Answer 1

You can create two HashMap s for storing the number of times an item was bought and the number of people that bought it, as well as a HashSet on each iteration so that the count of people buying an item will be correct even if the same person bought multiple of the same item. The statistics should only be printed at the end, after all the purchases have been accounted for.

final Map < String, Integer > numBought = new HashMap < > ();
final Map < String, Integer > peopleBought = new HashMap < > ();
for (int j = 0; j < numCustomers; j++) {
    // First and last name of each customer
    nameF[j] = scan.next();
    nameL[j] = scan.next();

    // Number of items bought
    final Set < String > vis = new HashSet < > ();
    int numItems = scan.nextInt();
    for (int k = 0; k < numItems; k++) {
        // For each number of items bought, name and quantity
        int numItemBought = scan.nextInt();
        String nameOfItem = scan.next();
        numBought.merge(nameOfItem, numItemBought, Integer::sum); // increase quantity of the item
        if (vis.add(nameOfItem))
            peopleBought.merge(nameOfItem, 1, Integer::sum); // increment number of people who bought this item
    }
}
for (final String item: itemName) {
    final Integer num = numBought.get(item);
    if (num == null) {
        System.out.println("No one bought " + item);
    } else {
        System.out.println(peopleBought.get(item) + " bought " + num + " " + item);
    }
}

Demo