121.md

121. Best Time to Buy and Sell Stock

Say you have an array for which the ith 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.

解析

遍历数组，并记下截止当前数字，最小的数值。那么当前能得到的收益就是当前数字-最小数值。

比较当前收益和之前最大收益，取最大值即可。

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