# 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
res := prices - 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
}