From 991d40ad2ef453c4d490844fd7eda6da58e548fc Mon Sep 17 00:00:00 2001
From: Roshan Mallick <roshanmallick2025@gmail.com>
Date: Thu, 16 Apr 2026 21:23:35 +0530
Subject: [PATCH] improve: replace recursive fibonacci with iterative optimized
 solution

---
 leetcode/src/509.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/leetcode/src/509.c b/leetcode/src/509.c
index 8129354bc5..275d9b0f05 100644
--- a/leetcode/src/509.c
+++ b/leetcode/src/509.c
@@ -1,8 +1,13 @@
-int fib(int N)
-{
-    if (N == 0)
-        return 0;
-    if (N == 1)
-        return 1;
-    return fib(N - 1) + fib(N - 2);
+int fib(int n) {
+    if (n <= 1) return n;
+
+    int a = 0, b = 1, c;
+
+    for (int i = 2; i <= n; i++) {
+        c = a + b;
+        a = b;
+        b = c;
+    }
+
+    return b;
 }