leetcode-----121. 买卖股票的最佳时机

• 链接：https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock/

算法1（暴力）

时间复杂度：\(O(n^2)\)

代码

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int ans = INT_MIN;
        if (prices.empty()) return 0;

        for (int i = 0; i < prices.size(); ++i) {
            for (int j = i; j < prices.size(); ++j) {
                ans = max(ans, prices[j] - prices[i]);
            }
        }
        return ans;
    }
};

算法2（优化）

时间复杂度：\(O(n)\)

代码

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int ans = 0;
        if (prices.empty()) return 0;
        int min_pro = prices[0];
        for (int i = 1; i < prices.size(); ++i) {
            if (prices[i] > prices[i - 1]) {
                ans = max(ans, prices[i] - min_pro);
            } else {
                min_pro = min(min_pro, prices[i]);
            }
        }
        return ans;
    }
};