LC#122 another approach- Best time to buy & sell stock problem, O(N) time, O(1) space

Author: NirmalSilwal

Leetcode/leetcodeTags/array/BestTimeToBuyAndSellStockII122.java

@@ -16,6 +16,35 @@ public static int maxProfit(int[] prices) {
 		return total;
 	}
 
+	// another approach to keep track of buy and selling date
+	public static int maxProfit2(int[] prices) {
+		if (prices.length < 2)
+			return 0;
+
+		int profit = 0;
+		int buyDate = 0, sellDate = 0;
+
+		for (int i = 1; i < prices.length; i++) {
+			if (prices[i] >= prices[i - 1]) {
+				// if stock price is increasing, we can sell current hold of
+				// stock in future with higher price
+				sellDate++;
+			} else {
+				// if stock graph starts to decrease, sell the previously hold
+				// stock
+				profit += (prices[sellDate] - prices[buyDate]);
+				// now set new buy and sell date to current date after
+				// collecting previous profits
+				buyDate = sellDate = i;
+			}
+		}
+
+		// now collecting profit from final increase in stock prices (final dip)
+		profit += (prices[sellDate] - prices[buyDate]);
+
+		return profit;
+	}
+
 	public static void main(String[] args) {
 
 		int[] prices = { 7, 1, 5, 3, 6, 4 };
@@ -24,5 +53,12 @@ public static void main(String[] args) {
 		System.out.println(maxProfit(new int[] { 1, 2, 3, 4, 5 }));
 		System.out.println(maxProfit(new int[] { 7, 6, 4, 3, 1 }));
 
+		// testing another approach
+		System.out.println();
+		System.out.println(maxProfit2(prices));
+
+		System.out.println(maxProfit2(new int[] { 1, 2, 3, 4, 5 }));
+		System.out.println(maxProfit2(new int[] { 7, 6, 4, 3, 1 }));
+
 	}
 }