leetcode(121-123)买股票的最佳时机

class Solution {
    public int maxProfit(int[] prices) {
        int len = prices.length;
        if(len<=1){
            return 0;
        }
        int min = prices[0];
        int max = 0;
        for(int i=1;i<len;++i){
            if(prices[i]-min>max){
               max =  prices[i]-min;
            }
            if(prices[i]<min){
               min = prices[i]; 
            } 
        }
        return max;
    }
}