# Leetcode 121. Best Time to Buy and Sell Stock – ￼

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.
```

## 解題步驟

1. 暴力雙迴圈
``````var maxProfit = function(prices) {

let maxProfit = 0;

for(let i = 0 ; i < prices.length;i++){
for(let j = i + 1 ; j < prices.length; j++){
let profit = prices[j] - prices[i]
if(profit > maxProfit){
maxProfit = profit;
}
}
}

return maxProfit
};``````

2. 根據題目特性，價格要買最低，賣價要賣最高

``````/**
* @param {number[]} prices
* @return {number}
*/
var maxProfit = function(prices) {