leetcode-121. Best Time to Buy and Sell Stock

Posted 2022-12-15 千念飞羽

leetcode-121. Best Time to Buy and Sell Stock

题目：

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 (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Example 1:
Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
Example 2:
Input: [7, 6, 4, 3, 1]
Output: 0

In this case, no transaction is done, i.e. max profit = 0.

题目是找最大收益的一次，方法也很简单，首先需要一个数组去维护当前坐标之前的最小值，然后用一个变量去记录当前值和当前值之前最小值之差就好。当然用两个变量也可以。

public class Solution 
    public int maxProfit(int[] prices) 
        if(prices.length<=1) return 0;

        int[] min = new int[prices.length];
        min[0] = prices[0];
        int ret = Integer.MIN_VALUE;
        for(int i = 1 ; i < min.length ; i++)
            min[i] = Math.min(min[i-1],prices[i]);
            ret = Math.max(ret,prices[i]-min[i]);
        
        return ret;