# LeetCode 121. Best Time to Buy and Sell Stock 原创Java参考解答

## 问题描述

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 (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Example 1:

```Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 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

In this case, no transaction is done, i.e. max profit = 0.
```

## 解题思路

prices[i2]为prices数组的最大值, prices[i1]为prices数组的最小值，i1 < i2。

## 参考代码

```public class Solution {
public int maxProfit(int[] prices) {
if (prices == null || prices.length == 0) {
return 0;
}

int maxProfit = 0;
int minPrice = Integer.MAX_VALUE;
for (int i = 0; i < prices.length; i++) {
maxProfit = Math.max(maxProfit, prices[i] - minPrice);
minPrice = Math.min(minPrice, prices[i]);
}

return maxProfit;
}
}
```

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