leetcode problem 121. Best Time to Buy and Sell Stock

Description

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 (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Note that you cannot sell a stock before you buy one.

Example 1:

Input: [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.
             Not 7-1 = 6, as selling price needs to be larger than buying price.

Example 2:

Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.

Solution

find the pair (a,b) that b-a are the greatest.

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int buy(INT_MIN),sell(0);
        for(int price:prices){
            buy = max(-price,buy);
            sell = max(buy+price,sell);  
        }
        return sell;
    }
};

result:

Runtime: 8 ms, faster than 99.32% of C++ online submissions for Best Time to Buy and Sell Stock.
Memory Usage: 9.6 MB, less than 42.03% of C++ online submissions for Best Time to Buy and Sell Stock.

20190404

tbc