From 8c7eb9b21f9bfb6cca917b4eec5aaf5c295e4f83 Mon Sep 17 00:00:00 2001
From: bali-ibrahim <balii@pm.me>
Date: Fri, 12 Jan 2024 01:23:02 +0300
Subject: [PATCH] dev: leetcode

---
 leetcode/509.fibonacci-number.go | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 leetcode/509.fibonacci-number.go

diff --git a/leetcode/509.fibonacci-number.go b/leetcode/509.fibonacci-number.go
new file mode 100644
index 0000000..711adcb
--- /dev/null
+++ b/leetcode/509.fibonacci-number.go
@@ -0,0 +1,19 @@
+func fib(n int) int {
+	var result [31]int
+	result[0] = 0
+	result[1] = 1
+
+	if n > 1 {
+		result[n] = tailRec(n, [2]int{result[0], result[1]})
+	}
+
+	return result[n]
+}
+
+func tailRec(n int, window [2]int) int {
+	if n == 1 {
+		return window[1]
+	}
+
+	return tailRec(n-1, [2]int{window[1], window[0] + window[1]})
+}