LeetCode 121: Best Time to Buy and Sell Stock

Best Time to Buy and Sell Stock

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.

解题思路

若在第 0,…,i−1 中的某一天买入，第 i 天卖出，那么能赚到的最大利润就是第 i 天的价格减去第 0,…,i−1 天中的最低价。

从前向后遍历数组，记录当前出现过的最低价格，作为买入价格，并计算以当天价格出售的收益，作为可能的最大收益，整个遍历过程中，出现过的最大收益就是所求。时间复杂度为 O(n)，代码如下：

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