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fix: replace right shift by using bit mask

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This commit is contained in:
JackyYin 2020-12-21 00:01:43 +08:00
parent e48f70db2b
commit a25febeb25
2 changed files with 13 additions and 12 deletions
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5
src/data-structures/hash-table/HashTable.js
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@ -70,8 +70,9 @@ export default class HashTable {
hash = (hash << 8) | hashPerRound; hash = (hash << 8) | hashPerRound;
} }
// Unsigned right shift to avoid negative number. // Bit mask to clear the left most bit,
hash >>>= 1; // so the result will be a positive number.
hash &= 0x7FFFFFFF;
// Reduce hash number so it would fit hash table size. // Reduce hash number so it would fit hash table size.
return hash % this.buckets.length; return hash % this.buckets.length;

20
src/data-structures/hash-table/__test__/HashTable.test.js
View File

@ -12,18 +12,18 @@ describe('HashTable', () => {
it('should generate proper hash for specified keys', () => { it('should generate proper hash for specified keys', () => {
const hashTable = new HashTable(); const hashTable = new HashTable();
expect(hashTable.hash('a')).toBe(9); expect(hashTable.hash('a')).toBe(18);
expect(hashTable.hash('b')).toBe(26); expect(hashTable.hash('b')).toBe(21);
expect(hashTable.hash('abc')).toBe(26); expect(hashTable.hash('abc')).toBe(21);
}); });
it('should set, read and delete data with collisions', () => { it('should set, read and delete data with collisions', () => {
const hashTable = new HashTable(3); const hashTable = new HashTable(3);
expect(hashTable.hash('a')).toBe(2); expect(hashTable.hash('a')).toBe(1);
expect(hashTable.hash('b')).toBe(2); expect(hashTable.hash('b')).toBe(2);
expect(hashTable.hash('c')).toBe(1); expect(hashTable.hash('c')).toBe(2);
expect(hashTable.hash('d')).toBe(2); expect(hashTable.hash('d')).toBe(1);
hashTable.set('a', 'sky-old'); hashTable.set('a', 'sky-old');
hashTable.set('a', 'sky'); hashTable.set('a', 'sky');
@ -38,8 +38,8 @@ describe('HashTable', () => {
const stringifier = (value) => `${value.key}:${value.value}`; const stringifier = (value) => `${value.key}:${value.value}`;
expect(hashTable.buckets[0].toString(stringifier)).toBe(''); expect(hashTable.buckets[0].toString(stringifier)).toBe('');
expect(hashTable.buckets[1].toString(stringifier)).toBe('c:earth'); expect(hashTable.buckets[1].toString(stringifier)).toBe('a:sky,d:ocean');
expect(hashTable.buckets[2].toString(stringifier)).toBe('a:sky,b:sea,d:ocean'); expect(hashTable.buckets[2].toString(stringifier)).toBe('b:sea,c:earth');
expect(hashTable.get('a')).toBe('sky'); expect(hashTable.get('a')).toBe('sky');
expect(hashTable.get('d')).toBe('ocean'); expect(hashTable.get('d')).toBe('ocean');
@ -94,7 +94,7 @@ describe('HashTable', () => {
hashTable.set('b', 'beta'); hashTable.set('b', 'beta');
hashTable.set('c', 'gamma'); hashTable.set('c', 'gamma');
expect(hashTable.getValues()).toEqual(['gamma', 'alpha', 'beta']); expect(hashTable.getValues()).toEqual(['alpha', 'beta', 'gamma']);
}); });
it('should get all the values from empty hash table', () => { it('should get all the values from empty hash table', () => {
@ -111,6 +111,6 @@ describe('HashTable', () => {
hashTable.set('ac', 'three'); hashTable.set('ac', 'three');
expect(hashTable.getValues()).toEqual(['one', 'three', 'two']); expect(hashTable.getValues()).toEqual(['three', 'one', 'two']);
}); });
}); });