Question

How to multiply every N consecutive items in a list with Java

Answer 1

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {

    public static List<Integer> productsNConsecutiveItems(List<Integer> lst, int n) {
        List<Integer> products = new ArrayList<>();

        if (n <= 0 || lst.size() < n) {
            return products; // empty
        }

        int outSize = lst.size() - n + 1;

        for (int i = 0; i < outSize; i++) {
            int prod = 1;

            // Multiply lst[i] * lst[i+1] * ... * lst[i+n-1]
            for (int j = 0; j < n; j++) {
                prod *= lst.get(i + j);
            }

            products.add(prod);

             // Example for n = 3:
             // 2 * 3 * 4  = 24
             // 3 * 4 * 5  = 60
             // 4 * 5 * 6  = 120
             // 5 * 6 * 7  = 210
             // 6 * 7 * 8  = 336
             // 7 * 8 * 9  = 504
             // 8 * 9 * 10 = 720
        }

        return products;
    }

    public static void main(String[] args) {
        List<Integer> lst = Arrays.asList(2, 3, 4, 5, 6, 7, 8, 9, 10);
        int n = 3;

        List<Integer> products = productsNConsecutiveItems(lst, n);

        System.out.println(products);
    }
}



/*
run:

[24, 60, 120, 210, 336, 504, 720]

*/

 

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