pythonic方法来修复滑动窗口中超出范围的索引

Question

我正在使用滑动窗口做这个 leetcode 问题，我意识到我得到了 IndexError，因为可以得到的最大值 j (= idx+1) 超出了范围。我想知道是否有一种优雅的方法来解决它？

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

问题陈述：

You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete as many transactions as you like (i.e., buy one and sell one share of the stock multiple times).

输入输出示例：

Input: prices = [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.

这是我的代码：

class Solution:
def maxProfit(self, prices: List[int]) -> int:
   
    totalProfit = 0
    currentProfit = 0
    
    for idx, x in enumerate(prices):
      
        j = idx+1
        
        while prices[j] > prices[idx] and prices[j] > prices[j-1]:
            
            currentProfit = prices[j] - prices[idx]
            totalProfit += currentProfit
            
            j += 1
 
    return totalProfit

错误信息：

IndexError: list index out of range
while prices[j] > prices[idx] and prices[j] > prices[j-1]:

编辑：正如@Prune 所建议的，当 j 在进入下一次迭代之前超出边界时，我会中断循环。它适用于示例输入，但我没有用极端情况测试它。让我们讨论一下是否还有改进的余地！

这是更新后的代码：

class Solution:
def maxProfit(self, prices: List[int]) -> int:
   
    totalProfit = 0
    currentProfit = 0
    
    for idx, x in enumerate(prices): 
      
        j = idx+1
        
        if j == len(prices): # boundary: break before entering loop
            break
        
        elif prices[j] > prices[idx] and prices[j] > prices[j-1]: # when continue to increase, enter loop

            currentProfit = prices[j] - prices[idx] # return value
            totalProfit += currentProfit # sum and return
      
            j += 1 #increase window size
            
    return totalProfit

Answer 1

这是你需要的吗？

from typing import List

def max_profit(prices: List[int]) -> int:
    profit = 0
    if len(prices) > 1: 
        bought_at = prices[0]
        for price in prices[1:]: 
            if bought_at and bought_at < price:
                print(f'sell at: {price} - bought at : {bought_at}')
                profit += (price - bought_at)
                bought_at = 0
            else:
                bought_at = price
    return profit     

result = max_profit([7,1,5,3,6,4])
print(f'profit: {result}')

输出：

$ python3 so.py
sell at: 5 - bought at : 1
sell at: 6 - bought at : 3
profit: 7