BestTimeToBuyandSellStockII.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).
*/


public class Solution {
    public int maxProfit(int[] prices) {
        if (prices==null || prices.length<=1){
            return 0;
        }
        
        // used to record max profit can get until each day
        int[] maxProfit=new int[prices.length];
        
        maxProfit[0]=0;
        
        for (int i=1; i<prices.length; i++){
            if (prices[i]>prices[i-1]){
                // price go up, max profit is max profit get by yesterday plus new profit
                maxProfit[i]=prices[i]-prices[i-1]+maxProfit[i-1];
            }    
            else{
              // price go down, max profit can get by today should be equal to yesterday.
                maxProfit[i]=maxProfit[i-1];
            }
        }
        
        
        return maxProfit[maxProfit.length-1];
    }
}