121. Best Time to Buy and Sell Stock

Easy
Array Dynamic Programming

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.

Example 1:

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.

Example 2:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.

Constraints:

  • 1 <= prices.length <= 10^5
  • 0 <= prices[i] <= 10^4
func maxProfit(prices []int) int {
	maxProfit := 0
	if len(prices) < 2 {
		return maxProfit
	}

	nextMax := prices[len(prices)-1]
	for i := len(prices) - 2; i >= 0; i-- {
		maxProfit = max(maxProfit, nextMax-prices[i])
		nextMax = max(nextMax, prices[i])
	}
	return maxProfit
}