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[DEV] Implementation of Hash Table Data Structure #1627
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| Original file line number | Diff line number | Diff line change |
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| export default class HashTable { | ||
| constructor(limit = 100) { | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. 100 seems very arbitrary. I'd force the user to choose for a fixed-size hash table. (I'd also make it clear that this is a fixed-size hash table (with dynamically grown buckets) as opposed to a dynamic hash table. In particular, a fixed-size hash table can't guarantee expected O(1) operations.)
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| // Initialize the storage and limit variables | ||
| this.storage = new Array(limit) | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. It would be helpful to call this property |
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| this.limit = limit | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This field is redundant with |
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| } | ||
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| // Hash function: | ||
| _hash(key, max) { | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Use the |
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| // Initialize the hash variable to 0 | ||
| let hash = 0 | ||
| // Iterate through the key and add the character code at each iteration to the hash variable | ||
| for (let i = 0; i < key.length; i++) hash += key.charCodeAt(i) | ||
| // Return the hash modulo the max | ||
| return hash % max | ||
| } | ||
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| // Insert a key-value pair into the hash table | ||
| set(key, value) { | ||
| // Hash the key | ||
| const index = this._hash(key, this.limit) | ||
| // If the index is empty, insert the key-value pair and create a bucket | ||
| if (this.storage[index] === undefined) this.storage[index] = [[key, value]] | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Use an object |
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| else { | ||
| // If the index is not empty, iterate through the bucket (collision handling) | ||
| let inserted = false | ||
| for (let i = 0; i < this.storage[index].length; i++) { | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Use a |
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| if (this.storage[index][i][0] === key) { | ||
| // If the key exists, update the value | ||
| this.storage[index][i][1] = value | ||
| inserted = true | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Just early |
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| } | ||
| } | ||
| // If the key does not exist, insert the key-value pair | ||
| if (inserted === false) this.storage[index].push([key, value]) | ||
| } | ||
| } | ||
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| // Get a value from the hash table | ||
| get(key) { | ||
| // Hash the key | ||
| const index = this._hash(key, this.limit) | ||
| // If the index is empty, return undefined | ||
| if (this.storage[index] === undefined) return undefined | ||
| else { | ||
| // If the index is not empty, iterate through the bucket | ||
| for (let i = 0; i < this.storage[index].length; i++) { | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Use a |
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| // If the key exists, return the value | ||
| if (this.storage[index][i][0] === key) return this.storage[index][i][1] | ||
| } | ||
| } | ||
| } | ||
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| // Remove a key-value pair from the hash table | ||
| remove(key) { | ||
| // Hash the key | ||
| const index = this._hash(key, this.limit) | ||
| // Check if the bucket exists | ||
| if (this.storage[index]) { | ||
|
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I'd use an early return here: |
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| // If the key matches the key at the index and there is only one item in the bucket, delete the bucket | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. (leaving an empty bucket behind wouldn't be an issue either; in fact i think the implementation may become slightly cleaner if you initialize all buckets to be empty, at a slight upfront performance cost at initialization) |
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| if ( | ||
| this.storage[index].length === 1 && | ||
| this.storage[index][0][0] === key | ||
| ) { | ||
| delete this.storage[index] | ||
| } else { | ||
| // If the index is not empty, iterate through the bucket | ||
| for (let i = 0; i < this.storage[index].length; i++) { | ||
| // If the key exists, delete the key-value pair | ||
| if (this.storage[index][i][0] === key) delete this.storage[index][i] | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. You're creating an array with holes here. I think this is rather dirty; it results in suboptimal time complexities (deleted items negatively affecting the time it takes to search a bucket). It would be cleaner to just take an entry from the end, swap the entry to be deleted with that, then pop the entry from the end. |
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| } | ||
| } | ||
| } | ||
| } | ||
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| // Check if a key exists in the hash table | ||
| has(key) { | ||
| // Hash the key to find the index | ||
| const index = this._hash(key, this.limit) | ||
| // Check if the bucket at the index exists | ||
| if (this.storage[index]) { | ||
| // Iterate through the bucket's key-value pairs | ||
| for (let i = 0; i < this.storage[index].length; i++) { | ||
| // Compare the current key with the target key and if the key is found, return true | ||
| if (this.storage[index][i][0] === key) return true | ||
| } | ||
| } | ||
| // If the key is not found, return false | ||
| return false | ||
| } | ||
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| // Print all keys/values in the table | ||
| printTable() { | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I don't think "print" helpers are good design. A debugger, or even just A better abstraction would be an "entries"-like method to iterate over all the key-value-pairs. |
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| for (let i = 0; i < this.storage.length; i++) { | ||
| if (this.storage[i] !== undefined) | ||
| console.log(`Bucket ${i}: ${JSON.stringify(this.storage[i])}`) | ||
| else console.log(`Bucket ${i} Empty`) | ||
| } | ||
| } | ||
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| // Clear all key/values | ||
| clear() { | ||
| this.storage = new Array(this.limit) | ||
| } | ||
| } | ||
| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,43 @@ | ||
| import HashTable from '../HashTable.js' | ||
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| describe('HashTable Data Structure Tests', () => { | ||
| test('HashTable Constructor', () => { | ||
| const hashTable = new HashTable(10) | ||
| expect(hashTable.limit).toBe(10) | ||
| expect(hashTable.storage.length).toBe(10) | ||
| }) | ||
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| test('HashTable get method', () => { | ||
| const hashTable = new HashTable(10) | ||
| expect(hashTable.get('key')).toBe(undefined) | ||
| }) | ||
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| test('HashTable set method', () => { | ||
| const hashTable = new HashTable(10) | ||
| hashTable.set('js', 'javascript') | ||
| expect(hashTable.get('js')).toBe('javascript') | ||
| }) | ||
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| test('HashTable remove method', () => { | ||
| const hashTable = new HashTable(10) | ||
| hashTable.set('js', 'javascript') | ||
| hashTable.remove('js') | ||
| expect(hashTable.get('js')).toBe(undefined) | ||
| }) | ||
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| test('HashTable has method', () => { | ||
| const hashTable = new HashTable(10) | ||
| hashTable.set('js', 'javascript') | ||
| expect(hashTable.has('js')).toBe(true) | ||
| }) | ||
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| test('HashTable clear method', () => { | ||
| const hashTable = new HashTable(10) | ||
| hashTable.set('js', 'javascript') | ||
| hashTable.set('ts', 'typescript') | ||
| hashTable.clear() | ||
| expect(hashTable.get('js')).toBe(undefined) | ||
| expect(hashTable.get('ts')).toBe(undefined) | ||
| expect(hashTable.storage).toEqual(new Array(10)) | ||
| }) | ||
| }) |