Say you have an array for which the ith element is the price of a given stock on day i.

maxProfit.java

/*
Say you have an array for which the ith element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions 
as you like (ie, buy one and sell one share of the stock multiple times). However, you 
may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
*/
import java.util.*;
public class Solution {
    Hashtable<Integer, Boolean> seen = new Hashtable<Integer, Boolean>();
    public int maxProfit(int[] prices) {
       // Start typing your Java solution below
       // DO NOT write main() function
        
        int size = prices.length;
        int max_price = 0;
        for(int i = 0; i < size; i++) {
            seen.clear();
            int price = getPrice(prices, i, size);
            if(price > max_price) {
                max_price = price;
            }
        }
        
        return max_price;
    }
   
    public int getPrice(int[] prices, int start, int end) {
        int total_price = 0;
        int first = prices[start];
        for(int i = start + 1; i < end; i++) {
            if(seen.containsKey(i)) continue;
            if(prices[i] > first) {
                total_price += (prices[i] - first);
            }
            total_price += getPrice(prices, i, end);
            seen.put(i, true);
        }
        return total_price;
    }
}

Not working for the large set.