# 121. Best Time to Buy and Sell Stock (Easy)

Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

Example 1:

```Input: [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.
Not 7-1 = 6, as selling price needs to be larger than buying price.
```

Example 2:

```Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.
```

## Solutions

``````class Solution {
// The key idea of this problem is to find the a combination of a preceding min price
// and a followup max price.
//
// Specifically, traverse the array and check whether the current price is lowest
// among all visited ones. If reach a relative min price, set to variable min.
// Move on and update the global max profit during iteration.

// Repeat pre-mentioned process once encounter another lower price than min.
public int maxProfit(int prices[]) {
int profit = 0;
int min = Integer.MAX_VALUE;

for (int i = 0; i < prices.length; i++) {
if (prices[i] < min) {
min = prices[i];
}

if (prices[i] - min > profit) {
profit = prices[i] - min;
}
}

return profit;
}
}
``````