解法一：动态规划

自己没想出来。。。
参见官方题解：https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/solution/mai-mai-gu-piao-de-zui-jia-shi-ji-han-shou-xu-fei-/

  1. class Solution {
  2.     public int maxProfit(int[] prices, int fee) {
  3.         // last保存上一次状态, cur保存当前状态
  4.         // 持有股票状态下的最大利润
  5.         int lastHold = -prices[0];
  6.         // 不持有股票状态下的最大利润
  7.         int lastCash = 0;
  8.         int curHold = lastHold;
  9.         int curCash = lastCash;
  10.         for (int i = 1; i < prices.length; ++i) {
  11.             curCash = Math.max(lastCash, lastHold + prices[i] - fee);
  12.             curHold = Math.max(lastHold, lastCash - prices[i]);
  13.             lastCash = curCash;
  14.             lastHold = curHold;
  15.         }
  16.         return Math.max(curHold, curCash);
  17.     }
  18. }