day 44: 121-best-time-to-buy-and-sell-stock

121-best-time-to-buy-and-sell-stock/driver.cpp

@@ -0,0 +1,10 @@
+#include "soln.hpp"
+
+int main()
+{
+	vector<int> prices{7, 1, 5, 3, 6, 4};
+	int answer = 5;
+	Solution soln;
+	cout << "Found max profit correctly? " << soln.test(prices, answer) << endl;
+	return 0;
+}

121-best-time-to-buy-and-sell-stock/soln.cpp

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+#include "soln.hpp"
+
+int Solution::maxProfit(vector<int> &prices)
+{
+	if (prices.size() == 1)
+		return 0;
+	int max_profit = 0, buying_day = 0, cur_profit = 0;
+	for (int i = 0; i < prices.size(); i++)
+	{
+		// cheaper buy day
+		if (prices[i] < prices[buying_day])
+			buying_day = i;
+		cur_profit = prices[i] - prices[buying_day];
+		// more profit
+		if (max_profit < cur_profit)
+			max_profit = cur_profit;
+	}
+	return max_profit;
+}
+
+bool Solution::test(vector<int> &prices, int answer)
+{
+	return maxProfit(prices) == answer;
+}

121-best-time-to-buy-and-sell-stock/soln.hpp

@@ -0,0 +1,8 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution
+{
+public:
+	int maxProfit(vector<int> &prices);
+	bool test(vector<int> &prices, int answer);
+};