# LeetCode : 0121. Best Time to Buy and Sell Stock (array)
###### tags:`leetcode`

#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <unordered_map>
using std::vector;
using std::unordered_map;
using namespace std;

class BaseVectorPrint {
    public:
        void BasePrint00(vector<int>& num) {
            for (size_t i = 0; i < num.size(); ++i) {
                cout << "[" <<num.at(i) << "]" << "; ";
            }
            cout << endl;
        }

        void BasePrint01(vector<int>& num) {
            for (size_t i = 0; i < num.size(); ++i) {
                cout << num[i] << "; ";
            }
            cout << endl;
        }

        void BasePrint02(vector<int>& num) {
            for (const auto &item : num) {
                cout << item << "; ";
            }
            cout << endl;
        }
        
        void TwoDimensionalPrint(vector<vector<int>> &num){
            for (int i = 0; i < num.size(); i++)
            {
                for (int j = 0; j < num[i].size(); j++)
                {
                    cout << "[" << num[i][j] << "]";
                }
                cout << endl;
            }
        }
};

class BaseSolution {
public:
    int maxProfit(vector<int>& prices) {
        int days = prices.size();
        int maxprofit = 0;
        int profit = 0;

        for(int i = 0 ; i < (days-1) ; i++){
            for (int j = i+1 ; j < days ; j++){
                profit = prices[j] - prices[i];
                //cout << "day " << i <<endl;
                cout << "profit" << profit << endl;
                    if(profit > maxprofit){
                        maxprofit = profit;
                        cout << "maxprofit = " << maxprofit << endl;
                    }
                }
        }
        return maxprofit;
    }
    //Time complexity: O(n^2)
    //Space complexity: O(1) 
};

class Solution01 {
public:
    int maxProfit(vector<int>& prices) {
        if(prices.empty()) return 0;
        int minprice = prices[0],
        int profitmax = 0;
        for(int i = 1; i < prices.size(); i++){
            //minprice = min(minprice, prices[i]);
            if (minprice > prices[i]){
                minprice = prices[i];
            }

            if (profitmax < (prices[i] - minprice)){
                profitmax = prices[i] - minprice;
            }
            //profit = max(profit, prices[i] - minprice);
        }
        return profitmax;
    }

    //Time complexity: O(n)
    //Space complexity: O(1) 

};


int main(void)
{
    BaseVectorPrint printVector;
    BaseSolution buy_and_sell_stock;
    Solution01 better_run;

    int ans = 0;

    vector<int> priceList01 = {7,1,5,3,6,4};
    vector<int> priceList02 = {7,6,4,3,1};
    

    //ans = buy_and_sell_stock.maxProfit(priceList01);
    ans = better_run.maxProfit(priceList01);
    cout << "maxProfit = " << ans << endl;
    printf("test\n");
    system("pause");
}

> save minprice space , use only one loop