121 买卖股票的最佳时机

https://leetcode.cn/leetbook/read/top-interview-questions-easy/xn8fsh/

https://leetcode.cn/problems/best-time-to-buy-and-sell-stock/description/

cost: 4m23s

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int r = 0;
        int minPrice = prices[0];
        for (const int& price : prices) {
            int v = price - minPrice;
            if (v < 0) {
                minPrice = price;
            } else if (v > r) {
                r = v;
            }
        }
        return r;
    }
};

• 时间复杂度：O(n)
• 空间复杂度：O(1)