Merge pull request #426 from sir-gon/feature/ctci_fibonacci_numbers

[Hacker Rank] Interview Preparation Kit: Recursion: Fibonacci Numbers…

docs/hackerrank/interview_preparation_kit/recursion_and_backtracking/ctci_fibonacci_numbers.md

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+# [Recursion: Fibonacci Numbers](https://www.hackerrank.com/challenges/ctci-fibonacci-numbers)
+
+- Difficulty:  `#easy`
+- Category: `#ProblemSolvingBasic`
+
+## The Fibonacci Sequence
+
+The Fibonacci sequence appears in nature all around us,
+in the arrangement of seeds in a sunflower and the spiral of a nautilus for example.
+
+The Fibonacci sequence begins with `fibonacci(0) = 0` and `fibonacci(1) = 1`
+as its first and second terms. After these first two elements,
+each subsequent element is equal to the sum of the previous two elements.
+
+Programmatically:
+
+- `fibonacci(0) = 0`
+- `fibonacci(1) = 1`
+- `fibonacci(n) = fibonacci(n - 1) + fibonacci(n - 2)`
+
+Given , return the  number in the sequence.
+
+## Example
+
+The Fibonacci sequence to `6` is `fs = [0, 1, 1, 2, 3, 5, 8]`.
+With zero-based indexing, `fs[5] = 5`.
+
+## Function Description
+
+Complete the recursive function `fibonacci` in the editor below.
+
+fibonacci has the following parameter(s):
+
+- `int n`: the index of the sequence to return
+
+## Returns
+
+- `int`: the  element in the Fibonacci sequence
+
+## Input Format
+
+The integer `n`.
+
+## Constraints
+
+- $ 0 \leq n \leq 30 $
+
+## Sample Input
+
+```text
+STDIN   Function
+-----   --------
+3       n = 3
+```
+
+## Sample Output
+
+```text
+2
+```
+
+## Explanation
+
+The Fibonacci sequence begins as follows:
+
+```C
+fibonacci(0) = 0
+fibonacci(1) = 1
+fibonacci(2) = (0 + 1) = 1
+fibonacci(3) = (1 + 1) = 2
+fibonacci(4) = (1 + 2) = 3
+fibonacci(5) = (2 + 3) = 5
+fibonacci(6) = (3 + 5) = 8
+```
+
+...
+
+In the sequence above, `fibonacci(3)` is `2`.

src/hackerrank/interview_preparation_kit/recursion_and_backtracking/ctci_fibonacci_numbers.test.ts

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+import { describe, expect, it } from '@jest/globals';
+import { logger as console } from '../../../logger';
+
+import { fibonacci } from './ctci_fibonacci_numbers';
+import TEST_CASES from './ctci_fibonacci_numbers.testcases.json';
+
+describe('ctci_fibonacci_numbers', () => {
+  it('fibonacci test cases', () => {
+    expect.assertions(3);
+
+    TEST_CASES.forEach((test) => {
+      const answer = fibonacci(test.input);
+
+      console.debug(`fibonacci(${test.input}) solution found: ${answer}`);
+
+      expect(answer).toStrictEqual(test.expected);
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/recursion_and_backtracking/ctci_fibonacci_numbers.testcases.json

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+[
+    {
+        "title": "Sample Test case 0",
+        "input": 5,
+        "expected": 5
+    },
+    {
+        "title": "Sample Test case 1",
+        "input": 12,
+        "expected": 144
+    },
+    {
+        "title": "Sample Test case 2",
+        "input": 17,
+        "expected": 1597
+    }
+]

src/hackerrank/interview_preparation_kit/recursion_and_backtracking/ctci_fibonacci_numbers.ts

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/recursion_and_backtracking/ctci_fibonacci_numbers.md]]
+ */
+
+export function fibonacci(n: number): number {
+  if (n == 0) {
+    return 0;
+  }
+  if (n == 1) {
+    return 1;
+  }
+
+  return fibonacci(n - 1) + fibonacci(n - 2);
+}
+
+export default { fibonacci };