BestTimeToBuyAndSellStock.cpp

/*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.
 */
 
class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int profit=0;
        if(prices.empty())
            return 0;
        int bought=prices[0];
        for(int i=1;i<prices.size();i++)
        {
            if(prices[i]>bought)
            {
                profit=max(profit,prices[i]-bought);
            }
            else
                bought=prices[i];
        }
        return profit;
    }
};