Fix Fibonacci problem for negative numbers (#55)

* handling fibonacci for negative numbers and 0

* fix fibonacci problem for negative numbers

Author: SumeetHaryani

README.md

@@ -30,6 +30,7 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
   - [Remove Consecutive Repeated Digits](src/_DataStructures_/Stack/remove-consecutive-repeated-digits)
   - [Implement 2 Stacks using Single Array](src/_DataStructures_/Stack/2-stacks-using1-array)
 
+
 - [Queue](src/_DataStructures_/Queue)
 
   - [Weave](src/_DataStructures_/Queue/weave)

src/_Classics_/fibonacci/index.js

@@ -2,8 +2,10 @@
 // the algorithm has time complexity of O(n^2), very bad!
 function fibonacci(position) {
   // if position is 1 or 2, the number in fibonacci sequence will be 1
-  if (position <= 1) {
+  if (position === 1 || position === 0) {
     return position;
+  } else if (position < 0) {
+    throw new Error('Invalid Position');
   }
 
   // else the element in fibonacci sequence will be the sum of
@@ -26,8 +28,11 @@ function fibonacciMemoized(index, cache) {
   if (cache[index]) {
     return cache[index];
   } else {
-    if (index <=1) {
+    if (index === 1 || index === 0) {
       return index;
+    } else if (index < 0) {
+      throw new Error('Invalid Position');
+
     } else {
       cache[index] =
         fibonacciMemoized(index - 1, cache) +
@@ -43,8 +48,10 @@ function fibonacciMemoized(index, cache) {
 
 function fibonacciTabular(n) {
   const table = [0, 1];
-  if (n <= 1) {
+  if (n === 1 || n === 0) {
     return n;
+  } else if (n < 0) {
+    throw new Error('Invalid Position');
   }
   for (let i = 2; i <= n; i += 1) {
     table[i] = table[i - 1] + table[i - 2];

src/_DataStructures_/Queue/index.js

@@ -17,4 +17,4 @@ class Queue {
   }
 }
 
-module.exports = Queue;
+module.exports = Queue;