lj fib brute force

.gitignore

@@ -0,0 +1 @@
+.idea

lib/fibonacci.rb

@@ -5,5 +5,30 @@
 # ....
 # e.g. 6th fibonacci number is 8
 def fibonacci(n)
-  raise NotImplementedError
+  if n.nil? || n < 0
+    raise ArgumentError
+    # sum the two previous numbers in sequence to the provided number
+  elsif n > 1
+    x = 1
+    fiba = 0
+    fibb = 1
+    while x < n
+      fibb = fiba + fibb
+      fiba = fibb - fiba
+      x += 1
+    end
+  elsif
+    fibb = n
+  end
+
+
+    return fibb
 end
+
+# sum the two previous numbers in sequence to the provided number
+fibonacci(12)
+
+# Time complexity is linear, as the while loop will run n times
+# Space complexity is constant as there will always be 3 variables,
+# one to store the iterator, one to store the first fibbonacci number
+# and one to store the second in the sequence