update book code

eBook/exercises/chapter_9/fibo/fibonacci.go

@@ -0,0 +1,33 @@
+package fibo
+
+/*
+func Fibonacci(n int) (res int) {
+	if n <= 1 {
+		res = 1
+	} else {
+		res = Fibonacci(n-1) + Fibonacci(n-2)
+	}
+	return
+}
+*/
+// accepts a general operation op:
+func Fibonacci(op string, n int) (res int) {
+	if n <= 1 {
+		switch op {
+			case "+":
+				res = 1
+			case "*":
+				res = 2
+			default: res = 0
+		}
+	} else {
+		switch op {
+			case "+":
+				res = Fibonacci(op, n-1) + Fibonacci(op, n-2)
+			case "*":
+				res = Fibonacci(op, n-1) * Fibonacci(op, n-2)
+			default: res = 0
+		}
+	}
+	return
+}