1 files changed, 43 insertions, 0 deletions
diff --git a/309/main.go b/309/main.go
new file mode 100644
index 0000000..e1b5dfb
--- /dev/null
+++ b/309/main.go
@@ -0,0 +1,43 @@
+package main
+
+import "fmt"
+
+func maxProfit(prices []int) int {
+	l := len(prices)
+	if l < 2 {
+		return 0
+	}
+
+	has1_doNothing := -prices[0]
+	has1_Sell := 0
+	has0_DoNothing := 0
+	has0_Buy := -prices[0]
+
+	for i := range prices {
+		if has1_doNothing > has0_Buy {
+			has1_doNothing = +has1_doNothing
+		} else {
+			has1_doNothing = +has0_Buy
+		}
+		// has1_doNothing = has1_doNothing > has0_Buy ? has1_doNothing : has0_Buy
+		has0_Buy = -prices[i] + has0_DoNothing
+		if has0_DoNothing > has1_Sell {
+			has0_DoNothing = +has0_DoNothing
+		} else {
+			has0_DoNothing = +has1_Sell
+		}
+		// has0_DoNothing = has0_DoNothing > has1_Sell ? has0_DoNothing : has1_Sell
+		has1_Sell = prices[i] + has1_doNothing
+	}
+
+	if has1_Sell > has0_DoNothing {
+		return has1_Sell
+	} else {
+		return has0_DoNothing
+	}
+}
+
+func main() {
+	fmt.Println(maxProfit([]int{1, 2, 3, 0, 2}))
+	fmt.Println(maxProfit([]int{1}))
+}