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

**Solution:**

```
class Solution {
public int maxProfit(int[] prices) {
int minprice = prices[0];
int maxprofit=0;
for(int i=0;i<prices.length;i++)
{
if(prices[i]<minprice) minprice=prices[i];
else if((prices[i]-minprice)>maxprofit)
{
maxprofit = prices[i]-minprice;
}
}
return maxprofit;
}
}
```

**Approach 2:**

```
class Solution
{
public int maxProfit(int[] prices)
{
int havingstock,nothavingstock;
havingstock = -prices[0];
nothavingstock =0;
for(int i=1;i<prices.length;i++)
{
havingstock = Math.max(havingstock,-prices[i]);
nothavingstock = Math.max(nothavingstock,havingstock+prices[i]);
}
return nothavingstock;
}
}
```

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