LeetCode link: 121. Best Time to Buy and Sell Stock

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

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

Input: prices = [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.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.

Input: prices = [7,6,4,3,1]

Output: 0

Explanation: In this case, no transactions are done and the max profit = 0.

• 1 <= prices.length <= 100000
• 0 <= prices[i] <= 10000

This problem can be solved using Dynamic programming.

Detailed solutions will be given later, and now only the best practices in 3 to 7 languages are given.

• Time: O(n).
• Space: O(n).

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        # states:
        #   0: hold stock
        #     1) keep holding
        #     2) today just bought
        #   1: no stock
        #     1) keep no stock
        #     2) today just sold
        dp = [-prices[0], 0]

        for price in prices[1:]:
            dc = dp.copy()

            dp[0] = max(dc[0], -price)
            dp[1] = max(dc[1], dc[0] + price)

        return dp[1]

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var maxProfit = function (prices) {
  const dp = [-prices[0], 0]

  for (let i = 1; i < prices.length; i++) {
    const dc = [...dp]

    dp[0] = Math.max(dc[0], -prices[i])
    dp[1] = Math.max(dc[1], dc[0] + prices[i])
  }

  return dp[1]
};

func maxProfit(prices []int) int {
    dp := []int{-prices[0], 0}

    for i := 1; i < len(prices); i++ {
        dc := slices.Clone(dp)

        dp[0] = max(dc[0], -prices[i])
        dp[1] = max(dc[1], dc[0] + prices[i])
    }

    return dp[1]
}

# Welcome to create a PR to complete the code of this language, thanks!

// Welcome to create a PR to complete the code of this language, thanks!

// Welcome to create a PR to complete the code of this language, thanks!