Memoization with fibonacci seq

README.md

@@ -16,3 +16,5 @@ Notably, this is an academic exercise. Many of these data structures are redunda
 - [Hash Table](./src/hash-table)
 - [Binary Search Tree](./src/binary-tree)
 - [Binary Heap](./src/binary-heap) (example MIN implementation)
+- [AVL Tree](./src/avl-tree)
+- [Memoization](./src/memoization/)

src/main.ts

@@ -4,3 +4,5 @@ export * from './stack'
 export * from './hash-table'
 export * from './binary-tree'
 export * from './binary-heap'
+export * from './avl-tree'
+export * from './memoization'

src/memoization/index.spec.ts

@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'bun:test'
+import { fibonacci } from '.'
+
+describe('Fibonacci Value Retrieval', () => {
+  it('should return 0 for the first index (0) in the Fibonacci sequence', () => {
+    expect(fibonacci(0)).toBe(0)
+  })
+
+  it('should return 1 for the second index (1) in the Fibonacci sequence', () => {
+    expect(fibonacci(1)).toBe(1)
+  })
+
+  it('should return 1 for the third index (2) in the Fibonacci sequence, as it is the sum of the two preceding numbers', () => {
+    expect(fibonacci(2)).toBe(1)
+  })
+
+  it('should return 2 for the fourth index (3) in the Fibonacci sequence, as it is the sum of the two preceding numbers', () => {
+    expect(fibonacci(3)).toBe(2)
+  })
+
+  it('should return 3 for the fifth index (4) in the Fibonacci sequence, as it is the sum of the two preceding numbers', () => {
+    expect(fibonacci(4)).toBe(3)
+  })
+
+  it('should return 5 for the sixth index (5) in the Fibonacci sequence, as it is the sum of the two preceding numbers', () => {
+    expect(fibonacci(5)).toBe(5)
+  })
+
+  it('should assume 0 for negative indices, as the Fibonacci sequence is not defined for negative numbers', () => {
+    expect(fibonacci(-1)).toBe(0)
+  })
+
+  it('should return 55 for the eleventh index (10) in the Fibonacci sequence, as it is the sum of the two preceding numbers', () => {
+    expect(fibonacci(10)).toBe(55)
+  })
+})

src/memoization/index.ts

@@ -0,0 +1,10 @@
+const memo: { [key: number]: number } = {}
+
+export const fibonacci = (n: number): number => {
+  if (n <= 0) return 0
+  if (n === 1) return 1
+  if (memo[n]) return memo[n]
+
+  memo[n] = fibonacci(n - 1) + fibonacci(n - 2)
+  return memo[n]
+}