fix: typo and handle range out

Author: JackyYin

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

@@ -56,21 +56,22 @@ export default class HashTable {
     // where charCodeAt(i) is the i-th character code of the key, n is the length of the key and
     // PRIME is just any prime number like 31.
     let hash = 0;
-    let hashPerRound;
 
     // Produce a 32-bits hash number.
     for (let i = 0; i < 4; i += 1) {
-      hashPerRound = table[(key.charCodeAt(0) + i) % 256];
-      for (let j = 0; j < key.legnth; j += 1) {
-        hashPerRound = table[hashPerRound ^ key[j]];
+      // charCodeAt may return number from 0 to 65536,
+      // should remap to range 0 to 255.
+      let hashPerRound = table[(key.charCodeAt(0) + i) % 256];
+      for (let j = 0; j < key.length; j += 1) {
+        hashPerRound = table[hashPerRound ^ (key.charCodeAt(j) % 256)];
       }
 
       // Left shift by 8-bits and OR the per-rounded hash.
       hash = (hash << 8) | hashPerRound;
     }
 
-    // Add max signed 32-bit number.
-    hash += ~(1 << 31);
+    // Unsigned right shift to avoid negative number.
+    hash >>>= 1;
 
     // Reduce hash number so it would fit hash table size.
     return hash % this.buckets.length;

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

@@ -12,16 +12,16 @@ describe('HashTable', () => {
   it('should generate proper hash for specified keys', () => {
     const hashTable = new HashTable();
 
-    expect(hashTable.hash('a')).toBe(17);
-    expect(hashTable.hash('b')).toBe(20);
-    expect(hashTable.hash('abc')).toBe(17);
+    expect(hashTable.hash('a')).toBe(20);
+    expect(hashTable.hash('b')).toBe(31);
+    expect(hashTable.hash('abc')).toBe(19);
   });
 
   it('should set, read and delete data with collisions', () => {
     const hashTable = new HashTable(3);
 
-    expect(hashTable.hash('a')).toBe(2);
-    expect(hashTable.hash('b')).toBe(0);
+    expect(hashTable.hash('a')).toBe(1);
+    expect(hashTable.hash('b')).toBe(1);
     expect(hashTable.hash('c')).toBe(0);
     expect(hashTable.hash('d')).toBe(2);
 
@@ -37,9 +37,9 @@ describe('HashTable', () => {
 
     const stringifier = (value) => `${value.key}:${value.value}`;
 
-    expect(hashTable.buckets[0].toString(stringifier)).toBe('b:sea,c:earth');
-    expect(hashTable.buckets[1].toString(stringifier)).toBe('');
-    expect(hashTable.buckets[2].toString(stringifier)).toBe('a:sky,d:ocean');
+    expect(hashTable.buckets[0].toString(stringifier)).toBe('c:earth');
+    expect(hashTable.buckets[1].toString(stringifier)).toBe('a:sky,b:sea');
+    expect(hashTable.buckets[2].toString(stringifier)).toBe('d:ocean');
 
     expect(hashTable.get('a')).toBe('sky');
     expect(hashTable.get('d')).toBe('ocean');
@@ -94,7 +94,7 @@ describe('HashTable', () => {
     hashTable.set('b', 'beta');
     hashTable.set('c', 'gamma');
 
-    expect(hashTable.getValues()).toEqual(['beta', 'gamma', 'alpha']);
+    expect(hashTable.getValues()).toEqual(['gamma', 'alpha', 'beta']);
   });
 
   it('should get all the values from empty hash table', () => {
@@ -111,6 +111,6 @@ describe('HashTable', () => {
 
     hashTable.set('ac', 'three');
 
-    expect(hashTable.getValues()).toEqual(['two', 'one', 'three']);
+    expect(hashTable.getValues()).toEqual(['one', 'two', 'three']);
   });
 });