# leetcode121 Best Time to Buy and Sell Stock

xiaoxiao2021-02-28  2

# 问题描述

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

If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

Example 1:

Input: [7,1,5,3,6,4]Output: 5Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.  Not 7-1 = 6, as selling price needs to be larger than buying price.Input: [7,6,4,3,1]Output: 0Explanation: In this case, no transaction is done, i.e. max profit = 0.

Example 2:

# 方法一

class Solution { public int maxProfit(int[] prices) { int max = 0; for(int i = 0; i < prices.length - 1; i++){ for(int k = i+1; k<prices.length;k++){ if(prices[i] - prices[k] >=0){ continue; } max = max > prices[k] - prices[i] ? max : prices[k] - prices[i]; } } return max; } }

# 方法二

class Solution { public int maxProfit(int[] prices) { if(prices.length ==0) return 0; int curmin = prices[0];//记录当前位置之前的最小元素 int curmax = 0;//当前位置的元素和当前最小元素的差值 int profitmax = 0;//整个数组范围内的最大利益值 for(int i = 1; i < prices.length; i++){ curmax = prices[i] - curmin; if(prices[i] < curmin) curmin = prices[i]; if(curmax > profitmax) profitmax = curmax; } return profitmax; } }