[LeetCode] 122. Best Time to Buy and Sell Stock II

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122. Best Time to Buy and Sell Stock II

Medium

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You are given an integer array prices where prices[i] is the price of a given stock on the ith day.

On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However, you can buy it then immediately sell it on the same day.

Find and return the maximum profit you can achieve.

 

Example 1:

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.
Total profit is 4 + 3 = 7.

Example 2:

Input: prices = [1,2,3,4,5]
Output: 4
Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
Total profit is 4.

Example 3:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: There is no way to make a positive profit, so we never buy the stock to achieve the maximum profit of 0.

 

Constraints:

• 1 <= prices.length <= 3 * 104
• 0 <= prices[i] <= 104

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Code

class Solution(object):
    def maxProfit(self, prices):
        dp = [0] * len(prices)
        for i in range(1, len(prices)):
            dp[i] = dp[i-1]
            if prices[i] > prices[i-1]:
                dp[i] += prices[i] - prices[i-1]

        return dp[-1]

최대 이익을 얻으려면, (어제 - 오늘) > 0을 만족하는 모든 경우에 발생하는 이익을 챙기면 된다.
즉, (어제 - 오늘) > 0이라면 주식을 파는 것이다.

Time Complexity