Merge pull request #77 from venkat-abhi/add-last-fib

add calculator for last digit of nth fibonacci number

Author: gouravthakur39

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;
+}