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`

Idea:

Tracking two variables – minStock(min price of the stock) and maxGain(max profit)

Solution:

``````/**
* @param {number[]} prices
* @return {number}
*/
var maxProfit = function(prices) {
let maxGain = 0;
let minStock = prices;

for (let i = 0; i < prices.length; i++) {
minStock = Math.min(minStock, prices[i]);
maxGain = Math.max(maxGain, prices[i] - minStock);
}
return maxGain;
};``````