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Commit ecd8d22

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committed
Add new hash table methods.
1 parent f04626b commit ecd8d22

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2 files changed

+82
-12
lines changed

2 files changed

+82
-12
lines changed

‎src/data-structures/hash-table/HashTable.js‎

Lines changed: 50 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,29 @@
11
import LinkedList from '../linked-list/LinkedList';
22

3+
// Hash table size directly affects on the number of collisions.
4+
// The bigger the hash table size the less collisions you'll get.
5+
// For demonstrating purposes hash table size is small to show how collisions
6+
// are being handled.
37
const defaultHashTableSize = 32;
48

59
export default class HashTable {
10+
/**
11+
* @param {number} hashTableSize
12+
*/
613
constructor(hashTableSize = defaultHashTableSize) {
714
// Create hash table of certain size and fill each bucket with empty linked list.
815
this.buckets = Array(hashTableSize).fill(null).map(() => new LinkedList());
16+
17+
// Just to keep track of all actual keys in a fast way.
18+
this.keys = {};
919
}
1020

11-
// Converts key string to hash number.
21+
/**
22+
* Converts key string to hash number.
23+
*
24+
* @param {string} key
25+
* @return {number}
26+
*/
1227
hash(key) {
1328
const hash = Array.from(key).reduce(
1429
(hashAccumulator, keySymbol) => (hashAccumulator + keySymbol.charCodeAt(0)),
@@ -19,8 +34,14 @@ export default class HashTable {
1934
return hash % this.buckets.length;
2035
}
2136

22-
insert(key, value) {
23-
const bucketLinkedList = this.buckets[this.hash(key)];
37+
/**
38+
* @param {string} key
39+
* @param {*} value
40+
*/
41+
set(key, value) {
42+
const keyHash = this.hash(key);
43+
this.keys[key] = keyHash;
44+
const bucketLinkedList = this.buckets[keyHash];
2445
const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
2546

2647
if (!node) {
@@ -32,8 +53,14 @@ export default class HashTable {
3253
}
3354
}
3455

56+
/**
57+
* @param {string} key
58+
* @return {*}
59+
*/
3560
delete(key) {
36-
const bucketLinkedList = this.buckets[this.hash(key)];
61+
const keyHash = this.hash(key);
62+
delete this.keys[key];
63+
const bucketLinkedList = this.buckets[keyHash];
3764
const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
3865

3966
if (node) {
@@ -43,10 +70,29 @@ export default class HashTable {
4370
return null;
4471
}
4572

73+
/**
74+
* @param {string} key
75+
* @return {*}
76+
*/
4677
get(key) {
4778
const bucketLinkedList = this.buckets[this.hash(key)];
4879
const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
4980

5081
return node ? node.value.value : null;
5182
}
83+
84+
/**
85+
* @param {string} key
86+
* @return {boolean}
87+
*/
88+
has(key) {
89+
return Object.hasOwnProperty.call(this.keys, key);
90+
}
91+
92+
/**
93+
* @return {string[]}
94+
*/
95+
getKeys() {
96+
return Object.keys(this.keys);
97+
}
5298
}

‎src/data-structures/hash-table/__test__/HashTable.test.js‎

Lines changed: 32 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -17,19 +17,23 @@ describe('HashTable', () => {
1717
expect(hashTable.hash('abc')).toBe(6);
1818
});
1919

20-
it('should insert, read and delete data with collisions', () => {
20+
it('should set, read and delete data with collisions', () => {
2121
const hashTable = new HashTable(3);
2222

2323
expect(hashTable.hash('a')).toBe(1);
2424
expect(hashTable.hash('b')).toBe(2);
2525
expect(hashTable.hash('c')).toBe(0);
2626
expect(hashTable.hash('d')).toBe(1);
2727

28-
hashTable.insert('a', 'sky-old');
29-
hashTable.insert('a', 'sky');
30-
hashTable.insert('b', 'sea');
31-
hashTable.insert('c', 'earth');
32-
hashTable.insert('d', 'ocean');
28+
hashTable.set('a', 'sky-old');
29+
hashTable.set('a', 'sky');
30+
hashTable.set('b', 'sea');
31+
hashTable.set('c', 'earth');
32+
hashTable.set('d', 'ocean');
33+
34+
expect(hashTable.has('x')).toBeFalsy();
35+
expect(hashTable.has('b')).toBeTruthy();
36+
expect(hashTable.has('c')).toBeTruthy();
3337

3438
const stringifier = value => `${value.key}:${value.value}`;
3539

@@ -47,18 +51,38 @@ describe('HashTable', () => {
4751
expect(hashTable.get('a')).toBeNull();
4852
expect(hashTable.get('d')).toBe('ocean');
4953

50-
hashTable.insert('d', 'ocean-new');
54+
hashTable.set('d', 'ocean-new');
5155
expect(hashTable.get('d')).toBe('ocean-new');
5256
});
5357

5458
it('should be possible to add objects to hash table', () => {
5559
const hashTable = new HashTable();
5660

57-
hashTable.insert('objectKey', { prop1: 'a', prop2: 'b' });
61+
hashTable.set('objectKey', { prop1: 'a', prop2: 'b' });
5862

5963
const object = hashTable.get('objectKey');
6064
expect(object).toBeDefined();
6165
expect(object.prop1).toBe('a');
6266
expect(object.prop2).toBe('b');
6367
});
68+
69+
it('should track actual keys', () => {
70+
const hashTable = new HashTable(3);
71+
72+
hashTable.set('a', 'sky-old');
73+
hashTable.set('a', 'sky');
74+
hashTable.set('b', 'sea');
75+
hashTable.set('c', 'earth');
76+
hashTable.set('d', 'ocean');
77+
78+
expect(hashTable.getKeys()).toEqual(['a', 'b', 'c', 'd']);
79+
expect(hashTable.has('a')).toBeTruthy();
80+
expect(hashTable.has('x')).toBeFalsy();
81+
82+
hashTable.delete('a');
83+
84+
expect(hashTable.has('a')).toBeFalsy();
85+
expect(hashTable.has('b')).toBeTruthy();
86+
expect(hashTable.has('x')).toBeFalsy();
87+
});
6488
});

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