【数据结构入门_数组】 Leetcode 121. 买卖股票的最佳时机

原题链接：Leetcode 121. Best Time to Buy and Sell Stock

You are given an array prices where prices[i] is the price of a given stock on the ith day.

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
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Example 2:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.
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Constraints:

• 1 <= prices.length <= 10⁵
• 0 <= prices[i] <= 10⁴

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方法一：模拟

思路：

遍历一遍数组，维护最低价格和最大利润

c++代码：

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int minprice = INT_MAX, maxProfit = 0;
        // 遍历的同时更新最低价格和最大利润
        for(auto price : prices){
            minprice = min(price, minprice);
            maxProfit = max(price - minprice, maxProfit);
        }
        return maxProfit;
    }
};
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复杂度分析：

• 时间复杂度：O(n)，需要遍历一遍数组
• 空间复杂度：O(1)，常数个临时变量