买卖股票的最佳时机 II Best Time to Buy and Sell Stock II

题目

给定一个数组,它的第 i 个元素是一支给定股票第 i 天的价格。设计一个算法来计算你所能获取的最大利润。你可以尽可能地完成更多的交易(多次买卖一支股票)。

以下为详细说明:

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.

https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-ii/

思路&题解

由于可以多次买卖,并且提前预知了每天的价格,只需要把每次低价卖高价卖的利润加和。 从图上看会比较直观,每次价格上涨都是一次买卖利润值。

122_maxprofit_1

public int maxProfit(int[] prices) {
    int sum = 0;
    for(int i = 1; i<prices.length; i++) {
        int diff = prices[i] - prices[i-1];
        if(diff > 0){
            sum +=diff;
        }
    }
    return sum;
}

知识点分析

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