LC#121 revised-best time to buy & sell stock problem, O(N) time O(1) space

Author: NirmalSilwal

Basic programs/revision/BestTimeToBuyAndSellStock121.java

@@ -0,0 +1,35 @@
+package practice.revisited;
+
+/*
+Input: prices = [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.
+Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
+ */
+
+public class BestTimeToBuyAndSellStock121 {
+
+	public static int maxProfit(int[] prices) {
+		if (prices.length < 2)
+			return 0;
+		int profit = 0;
+		int currlow = prices[0];
+		int sell = 0;
+
+		for (int curr = 1; curr < prices.length; curr++) {
+
+			if (prices[curr] < currlow) {
+				currlow = prices[curr];
+			}
+			sell = prices[curr] - currlow;
+			profit = Math.max(profit, sell);
+		}
+		return profit;
+	}
+
+	public static void main(String[] args) {
+		int[] prices = { 7, 1, 5, 3, 6, 4 };
+		System.out.println(maxProfit(prices));
+		System.out.println(maxProfit(new int[] { 7, 6, 4, 3, 1 }));
+	}
+}