FindMaximumSellProfit.java

package arrays;


import com.sun.tools.javac.util.Pair;

public class FindMaximumSellProfit {

    /*
     * Given an array representing prices of the stock on different days,
     * find the maximum profit that can be earned by performing maximum of one transaction.
     * A transaction consists of activity of buying and selling the stock on different or same days.
     *
     * Eg: 1 - {100, 80, 120, 130, 70, 60, 100, 125}
     * the price of the stock on day-1 is 100, on day-2 is 80 and so on.
     * The maximum profit that could be earned in this window is 65 (buy at 60 and sell at 125).
     *
     * Eg: 2 - For price array - {100, 80, 70, 65, 60, 55, 50}, maximum profit that could be earned is 0.
     *
     * */


    public static int findMaximumProfit(int[] stockPrices) {
        int minimumPrice = Integer.MAX_VALUE;
        int maxProfit = 0;

        /*
         * The profit is the maximum value of the maximumProfit so far and
         * the difference between the current element(selling price) and the minimum buying price - i.e. profit for that buy
         * Profit = current selling price - the minimum buying price
         *
         * Minimum buying price is the minimum value between the current element and the minimum price
         * */
        for(int i=0; i<stockPrices.length; i++) {
            maxProfit = Math.max(maxProfit, stockPrices[i]-minimumPrice);
            minimumPrice = Math.min(minimumPrice, stockPrices[i]);
        }

        return maxProfit;
    }



















    public static Pair<Integer, Integer> findMaximumSellProfit(int length, int[] arr) {
        int currentBuy = arr[0];
        int globalSell = arr[1];
        int globalProfit = globalSell - currentBuy;

        int currentProfit;

        for(int i=1; i< length; i++) {
            int currentSell = arr[i];
            currentProfit = currentSell - currentBuy;

            if(currentProfit > globalProfit) {
                globalProfit = currentProfit;
                globalSell = arr[i];
            }

            if(currentBuy > arr[i]) {
                currentBuy = arr[i];
            }
        }

        int optimalBuyPrice = globalSell-globalProfit;
        int optimalSellPrice = globalSell;
        return Pair.of(optimalBuyPrice, optimalSellPrice) ;
    }





    public static void main(String[] args) {
        int[] arr = {100, 80, 120, 130, 70, 60, 100, 125};
        System.out.println(findMaximumSellProfit(arr.length, arr));
        System.out.println(findMaximumProfit(arr));
    }
}