Add hashmap

Author: Hugo Venega

src/hashmap/hashmap.spec.ts

@@ -0,0 +1,27 @@
+import HashMap from './hashmap';
+
+interface TestElement {
+  n : number
+}
+describe('HashMaP', () => {
+  let hashmap: HashMap<TestElement>;
+  beforeEach(() => {
+    hashmap = new HashMap <TestElement>();
+  });
+
+  it('should add an element into the Hashmap', () => {
+    hashmap.set('pepe', { n: 12 });
+    expect(hashmap.length).toEqual(1);
+  });
+  it('should return the requested item', () => {
+    hashmap.set('pepe', { n: 12 });
+    expect(hashmap.get('pepe')).toEqual({ key: 'pepe', value: { n: 12 } });
+  });
+  it('should return undefined when the key not hashed', () => {
+    expect(hashmap.get('zapallo')).toEqual(undefined);
+  });
+  it('returns undefined when the key collides but is not found', () => {
+    hashmap.set('pepe', { n: 12 });
+    expect(hashmap.get('coco')).toEqual(undefined);
+  });
+});

src/hashmap/hashmap.ts

@@ -0,0 +1,51 @@
+import BinarySearchTree from '../tree/BST/binarySearchTree';
+
+interface HashMapElement<T>{
+  key: string,
+  value?: T
+}
+
+const ARRAY_SIZE = 1000;
+
+export default class HashMap<T = any> {
+  private memory : BinarySearchTree<HashMapElement<any>>[] = [];
+
+  public length = 0;
+
+  private compareFunction = (a: { key: string },
+    b:HashMapElement<any>): number => a.key.localeCompare(b.key);
+
+  set(key: string, value: T): void {
+    const placeToAdd = this.hashFunction(key) % ARRAY_SIZE;
+    if (!this.memory[placeToAdd]) {
+      this.memory[placeToAdd] = new BinarySearchTree<HashMapElement<any>>(this.compareFunction);
+    }
+    this.memory[placeToAdd].add({ key, value });
+    this.length += 1;
+  }
+
+  get(key: string): HashMapElement<any> | undefined {
+    const positionInArray = this.hashFunction(key) % ARRAY_SIZE;
+    const treeInArray = this.memory[positionInArray];
+    if (!treeInArray) {
+      return undefined;
+    }
+    const result = treeInArray.search({ key });
+    if (!result) {
+      return undefined;
+    }
+    return result;
+  }
+
+  private hashFunction(key: string): number {
+    let hashValue = 0;
+    const stringKey = key.toString();
+
+    for (let index = 0; index < stringKey.length; index += 1) {
+      const charCode = stringKey.charCodeAt(index);
+      hashValue += charCode;
+    }
+
+    return hashValue;
+  }
+}