Best Time to Buy and Sell Stock II LeetCode

You are given an integer array prices where prices[i] is the price of a given stock on the ith day.

On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However, you can buy it then immediately sell it on the same day.

Find and return the maximum profit you can achieve.

 Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 7
Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5), profit = 5-1 = 4.
Then buy on day 4 (price = 3) and sell on day 5 (price = 6), profit = 6-3 = 3.
Total profit is 4 + 3 = 7.

Example 2:

Input: prices = [1,2,3,4,5]
Output: 4
Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
Total profit is 4.

Example 3:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: There is no way to make a positive profit, so we never buy the stock to achieve the maximum profit of 0.

 NOTE:

• 1 <= prices.length <= 3 * 104
• 0 <= prices[i] <= 104

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 (i.e, you must sell the stock before you buy again).

This problem is popular in LeetCode

Solution: Source: 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 (i.e., buy one and sell one share of the stock multiple times).
	Note: You may not engage in multiple transactions at the same time (i.e., you must sell the stock before you buy again).
	Example 1:
	Input: [7,1,5,3,6,4]
	Output: 7
	Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5), profit = 5-1 = 4.
	Then buy on day 4 (price = 3) and sell on day 5 (price = 6), profit = 6-3 = 3.
	Example 2:
	Input: [1,2,3,4,5]
	Output: 4
	Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
	Note that you cannot buy on day 1, buy on day 2 and sell them later, as you are
	engaging multiple transactions at the same time. You must sell before buying again.
	Example 3:
	Input: [7,6,4,3,1]
	Output: 0
	Explanation: In this case, no transaction is done, i.e. max profit = 0.
	*/
	import java.lang.Integer;
	import java.util.Arrays;
	public class BestTimeToBuySellStockII{
	/**
	Method2:
	-we take the daily prices array and accumulate the profit if the sequence is increasing
	O(n), Space O(1)
	*/
	public static int findMaxProfit2(int[] prices){
	int total = 0;
	for (int i=0; i< prices.length-1; i++) {
	if (prices[i+1]>prices[i]) total += prices[i+1]-prices[i];
	}
	return total;
	}
	public static void main(String args[]){
	int[] nums = new int[]{7,1,5,3,6,4};//diff is {-6, 4, -2, 3, -2}
	nums = new int[]{7,6,4,3,1};
	nums = new int[]{1,2,3,4,5};
	System.out.println("the maxprofit2 is:"+findMaxProfit2(nums));
	}
	}

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