## Challenge Statement

- 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**to sell that stock in the future. - Return
*the maximum profit you can achieve from this transaction*. If you cannot achieve any profit, return 0. - This challenge corresponds to LeetCode #121.

### Constraints

`1 <= prices.length <= 10`

^{5}`0 <= prices[i] <= 10`

^{4}

**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.

## Solution

Below is my solution and some test cases. This solution has a **linear time complexity O(n) and a constant space complexity O(1)**, where n is the length of the input list*. *