add: Best Time to Buy and Sell Stock

BestTimetoBuyandSellStock/step1.md

@@ -0,0 +1,26 @@
+```go
+// For each day, 
+// We need to check if it's day that we can buy the stock with lower price
+// And then check what if we sell it with the lowest price that we found in the past
+// Time complexity:  O(N) N: number of prices
+// Space complexity: 1
+// Time spend: 04:32
+func maxProfit(prices []int) int {
+    buy := -prices[0];
+    sell := buy + prices[0];
+
+    for _, p := range prices {
+        buy = max(buy, -p)
+        sell = max(sell, buy + p)
+    }
+
+    return sell
+}
+
+func max(a, b int) int {
+    if a > b {
+        return a
+    }
+    return b
+}
+```

BestTimetoBuyandSellStock/step2.md

@@ -0,0 +1,21 @@
+```go
+// Time spend: 01:10
+func maxProfit(prices []int) int {
+	buy := -prices[0]
+	sell := buy + prices[0]
+
+	for _, p := range prices {
+		buy = max(buy, -p)
+		sell = max(sell, buy + p)
+	}
+
+	return sell
+}
+
+func max(a, b int) int {
+	if a < b {
+		return b
+	}
+	return a
+}
+```

BestTimetoBuyandSellStock/step3.md

@@ -0,0 +1,71 @@
+```go
+// Time spend: 01:00
+package main
+func maxProfit(prices []int) int {
+	buy := -prices[0]
+	sell := buy + -prices[0]
+
+	for _, p := range prices {
+		buy = max(buy, -p)
+		sell = max(sell, buy + p)
+	}
+
+	return sell
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+```
+
+```go
+// Time spend: 01:02
+package main
+func maxProfit(prices []int) int {
+	buy := -prices[0]
+	sell := buy + -prices[0]
+
+	for _, p := range prices {
+		buy = max(buy, -p)
+		sell = max(sell, buy + p)
+	}
+
+	return sell
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+```
+
+```go
+// Time spend: 00:55
+package main
+func maxProfit(prices []int) int {
+	buy := -prices[0]
+	sell := buy + -prices[0]
+
+	for _, p := range prices {
+		buy = max(buy, -p)
+		sell = max(sell, buy + p)
+	}
+
+	return sell
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+```