[LeetCode] 121. Best Time to Buy and Sell Stock

题目链接：传送门

Description

Say you have an array for which the i^th element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Example 1:

Input: [7, 1, 5, 3, 6, 4]

Output: 5
max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)

Example 2:

Input: [7, 6, 4, 3, 1]

Output: 0
In this case, no transaction is done, i.e. max profit = 0.

Solution

题意：

已知 n 天的股票价格，求仅买卖一次能获得的最高利润，注意先买后卖

思路：

求一个前缀最小值，再枚举一遍即可

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