Problem

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 (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

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.

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

Code

static int var = [](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();
class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int max = 0;
        int temp = 0;
        int len = prices.size();
        vector<int> tempvec;
        if(len > 0)
            for(int i=1;i<len;i++){                
                tempvec.push_back(prices[i]-prices[i-1]);
            }
            for(int i=0;i<len-1;i++){
                temp+=tempvec[i];
                if(temp > max)
                    max = temp;
                if(temp < 0)
                    temp = 0;
            }
        return max;
    }
};

Result

121. Best Time to Buy and Sell Stock.png