From d29d92cabd15f9375c2ce96f2a32085158bab62e Mon Sep 17 00:00:00 2001
From: venkat-abhi <venkat.abhishek.1999@gmail.com>
Date: Mon, 7 Oct 2019 19:49:57 +0530
Subject: [PATCH] add calculator for last digit of nth fibonacci number

---
 last-digit-fibonacci.c | 43 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 last-digit-fibonacci.c

diff --git a/last-digit-fibonacci.c b/last-digit-fibonacci.c
new file mode 100644
index 0000000..bc665d5
--- /dev/null
+++ b/last-digit-fibonacci.c
@@ -0,0 +1,43 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+int last_digit_fib_optimized(const int index)
+{
+	int first = 0; 
+	int second = 1;
+	int current = 0;
+
+	for (int i = 2; i <= index; ++i) {
+		current = (first + second) % 10;
+		first = second;
+		second = current;
+	}
+
+	return (current);
+}
+
+/* This is the direct solution for reference */
+int last_digit_fib_naive(const int index)
+{
+	int *arr;
+	arr = (int *)malloc((index+1) * sizeof(int));
+	arr[0] = 0;
+	arr[1] = 1;
+
+	for (int i = 2; i <= index; ++i) { // store only the last digit of each index
+		arr[i] = (arr[i - 1] + arr[i - 2]) % 10;
+	}
+
+	int res = arr[index];
+	return (res);
+}
+
+int main(int argc, char **argv)
+{
+	int index = 0;
+	scanf("%d", &index);
+
+	printf("%d\n", last_digit_fib_optimized(index));
+	
+	return 0;
+}
\ No newline at end of file