### LeetCode Challenge #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.
```

Constraints:

• `1 <= prices.length <= 105`
• `0 <= prices[i] <= 104`
##### Video Solution
###### Java Solution
```				```
class Solution {
public int maxProfit(int[] prices) {
int n = prices.length;
int[] maxValue = new int[n];
maxValue[n-1] = prices[n-1];

for(int i = n-2 ; i>=0;i--){
maxValue[i] = Math.max(maxValue[i+1],prices[i]);
}

int ans = 0 ;
for(int i=0;i<prices.length ;i++){
int currPro = maxValue[i] - prices[i];
ans = Math.max(ans , currPro);
}
return ans ;
}
}
```
```