Leetcode121 Best Time to Buy and Sell Stock

题目描述

Example 1:

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

Example 2:

1
2
3

Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.

思路

思路：两个数组，一个数组储存最低价格，一个数组储存最高价格，最大的价格对应的位置要比最小的价格对应的位置靠后（值大），最小数组的值是当前值与最小数组里的最后一个元素比较，更小的那一个放入最小价格数组；当前位置的价格与最大数组的最后一个元素比较，较大的价格放入最大数组中。直接返回最最大价格数组里的最后一个元素。

代码

class Solution {
    public int maxProfit(int[] prices) {
        if(prices.length<1) return 0;
        int[] lowprice= new int[prices.length];
        int[] highprice= new int[prices.length];
        lowprice[0]=prices[0];
        highprice[0]=0;
        for(int i=1;i<prices.length;i++){
            lowprice[i]=Math.min(prices[i],lowprice[i-1]);
            highprice[i]=Math.max(highprice[i-1],prices[i]-lowprice[i-1]);
        }
        return highprice[prices.length-1];
    }
}