二刷121. Best Time to Buy and Sell Stock

Easy题，就不说暴力解了. 求minDiff我们控制变量，找最小被减数，差就会最大。这样遍历一次，一边更新最小被减数，一边更新最大差值。

public class Solution {
    /*
     * @param prices: Given an integer array
     * @return: Maximum profit
     */
    public int maxProfit(int[] prices) {
        // write your code here
        if (prices == null || prices.length == 0){
            return 0;
        }
        int min = prices[0];
        int maxDiff = 0;
        for (int i = 1; i < prices.length; i++){
            if (prices[i] < min){
                min = prices[i];
            } else {
                maxDiff = Math.max(maxDiff, prices[i] - min);
            }
        }
        return maxDiff;
    }
}