Handle negatives

README.md

@@ -38,7 +38,7 @@ Tests are always supposed to be right and you should not need to edit them at an
 
 The goal state of this exercise is a `main` branch that contains all of the features that are currently split onto separate feature branches. **You should not have to write or modify any code outside of the merge conflict resolution process.**
 
-To get familiar with git and remote git repositories, there are several different approaches you can take to resolving these conflicts. I'd recommend working through them in order - the first one is the most refective of the process that we'll use on the project, but the others are great practice.
+To get familiar with git and remote git repositories, there are several different approaches you can take to resolving these conflicts. I'd recommend working through them in order - the first one is the most refective of the standard development process on a multi-developer project, but the others are great practice.
 
 Before starting to resolve the conflicts on each branch, it's a good idea to take a look through the changes and make sure you understand how the new code and test(s) on the branch work.
 
@@ -47,9 +47,9 @@ Before starting to resolve the conflicts on each branch, it's a good idea to tak
     - Most of the time, it won't let you merge it because of a conflict
     - Locally, pull an up-to-date version of `main` and rebase the feature branch on top of it, resolving any conflicts as they arise
     - Force push your feature branch. It should now be possible to merge the PR that you previously created
-        - **Note:** Force pushing is quite dangerous, and you shouldn't get into the habit of doing it other than for this specific case where a branch has been rebased and you need to update the remove version. On our project, the `main` branch will be protected against force pushing.
+        - **Note:** Force pushing is quite dangerous, and you shouldn't get into the habit of doing it other than for this specific case where a branch has been rebased and you need to update the remove version. In many remote repositories, the `main`/`master` branch is protected against force pushing for this reason.
 2. Without using GitHub, get all of the features on to the `main` branch only using `git merge` commands.
-3. Without using GitHub, get all of the features on to the `main` branch only using `git rebase` commands.
+3. Without using GitHub, get all of the features onto a single branch only using `git rebase` commands (this branch doesn't have to be `main`).
 
 After each run-through, you will want to revert your repository back to its starting state. You might want to explore ways of doing this (without re-forking the original repo), for example:
 

src/fibonacci.ts

@@ -1,11 +1,18 @@
 export const computeFibonacciNumber = (position: number): number => {
-    let i = 1;
-    let j = 1;
+    if (position === 0) {
+        return 0;
+    }
+    if (position < 0) {
+        return computeNegativeFibonacci(position);
+    }
 
     if (position <= 2) {
         return 1;
     }
 
+    let i = 1;
+    let j = 1;
+
     let currentPosition = 2;
     while (currentPosition < position) {
         const temp = i;
@@ -15,3 +22,12 @@ export const computeFibonacciNumber = (position: number): number => {
     }
     return j;
 };
+
+const computeNegativeFibonacci = (position: number): number => {
+    if (position >= 0) {
+        throw new Error(`Position must be less than zero! Received: ${position}.`);
+    }
+    const resultIsNegative = position % 2 === 0;
+    const absoluteResult = computeFibonacciNumber(-position);
+    return resultIsNegative ? absoluteResult * -1 : absoluteResult;
+}

tests/negativeFibonacci.test.ts

@@ -0,0 +1,11 @@
+import { computeFibonacciNumber } from '../src/fibonacci';
+
+describe('Negative Fibonacci Test', () => {
+    it('Check negative fibonacci works for small negative numbers', () => {
+        const inputs = [-6, -5, -4, -3, -2, -1]
+        const expectedOutputs = [-8, 5, -3, 2, -1, 1];
+        for (let i = 0; i < expectedOutputs.length; i++) {
+            expect(computeFibonacciNumber(inputs[i])).toEqual(expectedOutputs[i]);
+        }
+    });
+})