121. Best Time to Buy and Sell Stock

Easy

You are given an array prices where prices[i] is the price of a given stock on the ith 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 <= 105

• 0 <= prices[i] <= 104

解題

func maxProfit(prices []int) int {
    if len(prices) <= 1 { return 0 }

    min := prices[0]
    res := prices[1] - min

    for i:=1; i<len(prices); i++ {
        if prices[i] - min > res {
            res = prices[i] - min
        }

        if prices[i] < min {
            min = prices[i]
        }
    }

    if res < 0 { return 0 }
    return res
}