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.
解题思路：
本题目是《算法导论》 4.1 节 给出的股票问题的原题，可以转化为最大子数组的问题，书本上给出的是分治的做法，练习4.1-5给出了线性时间的算法。
Java for LeetCode 053 Maximum Subarray实现了相应的解法，如果不转化为最大子数组问题，解法如下：
一次遍历，每次找到最小的Buy点即可，JAVA实现如下：
public int maxProfit(int[] prices) {
int buy = 0;
int profit = 0;
for (int i = 0; i < prices.length; ++i) {
if (prices[buy] > prices[i])
buy = i;
profit = Math.max(profit, prices[i] - prices[buy]);
}
return profit;
}