leetcode 121 Best Time to Buy and Sell Stock

//dp 时间复杂度O(n) 空间复杂度O(1)
class Solution {
public:
    int maxProfit(vector<int>& prices) {
        if(prices.size()==0) return 0;
        int minVal = 0, minNum = prices[0];
        for(int i=1;i<prices.size();++i){
            int tmp = prices[i]-minNum;
            minVal = max(minVal, tmp);
            minNum = min(prices[i], minNum);
        }
        return minVal;
    }
};