Solution.java

package hackrank.algorithm.dynamic.maxstock;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

/**
 * Stock Maximize Challenge
 *
 * @see https://www.hackerrank.com/challenges/stockmax
 */
public class Solution {

    public static void main(String[] args) {

        for (List<Integer> prices : readInput(System.in)) {
            System.out.println(calcMaxProfit(prices));
        }

    }

    public static long calcMaxProfit(List<Integer> prices) {

        long cost = 0;
        long profit = 0;
        long stocks = 0;

        int max = -1;
        for (int i = 0; i < prices.size(); i++) {
            if (max == -1) {
                max = findMax(prices, i);
            }

            int price = prices.get(i);
            if (price == max) {
                profit += price * stocks;
                stocks = 0;
                max = -1;
            } else {
                cost += price;
                stocks++;
            }
        }

        return profit - cost;
    }

    private static int findMax(List<Integer> prices, int start) {
        int max = -1;
        for (int i = start; i < prices.size(); i++) {
            int price = prices.get(i);
            if (price > max) {
                max = price;
            }
        }

        return max;
    }

    public static List<List<Integer>> readInput(InputStream stream) {

        Scanner scanner = new Scanner(stream);

        int testCases = scanner.nextInt();
        List<List<Integer>> data = new ArrayList<>(testCases);

        for (int t = 0; t < testCases; t++) {
            int size = scanner.nextInt();
            List<Integer> prices = new ArrayList<>(size);

            for (int i = 0; i < size; i++) {
                prices.add(scanner.nextInt());
            }

            data.add(prices);
        }

        scanner.close();

        return data;
    }

}