Commit aa5fd54

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change hash fn to use prime num to minimize collisions, add separate chaining collision handling

1 parent 6a1186c commit aa5fd54Copy full SHA for aa5fd54

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+42

-11

lines changed

+42

-11

lines changed

Lines changed: 11 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -2,11 +2,19 @@`
`2`	`2`	`Object.defineProperty(exports, "__esModule", { value: true });`
`3`	`3`	`class HashTable {`
`4`	`4`	`constructor() {`
`5`		`- this.hash = (value,max) => {`
	`5`	`+ this.hash = (key,arrLen) => {`
`6`	`6`	`// naive hash fn for illustrative purposes`
`7`		`- if (max <= 0)`
	`7`	`+ if (arrLen <= 0)`
`8`	`8`	`throw TypeError('Max hash value must be a positive integer');`
`9`		`- return value.split('').reduce((a, b) => a * b.charCodeAt(0), 1) % max;`
	`9`	`+ let total = 0;`
	`10`	`+ let prime = 31;`
	`11`	`+ for (let i = 0; i < Math.min(key.length, 100); i++) {`
	`12`	`+ let char = key[i];`
	`13`	`+ let value = char.charCodeAt(0) - 96;`
	`14`	`+ total = (total * prime + value) % arrLen;`
	`15`	`+ }`
	`16`	`+ return total;`
	`17`	`+ // return value.split('').reduce((a, b) => a * b.charCodeAt(0), 1) % max;`
`10`	`18`	`};`
`11`	`19`	`}`
`12`	`20`	`}`

Lines changed: 5 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,11 @@ describe('basic hash table', () => {`
`12`	`12`	`});`
`13`	`13`	`test('hash fn takes string and returns number between 0 and specified max', () => {`
`14`	`14`	`const max = 50;`
`15`		`- expect(HT.hash('test', max)).toBeLessThan(50);`
	`15`	`+ let str = '';`
	`16`	`+ for (let i = 0; i < 100; i++) {`
	`17`	`+ str += String.fromCharCode(Math.floor(Math.random() * (200 - 1) + 1));`
	`18`	`+ }`
	`19`	`+ expect(HT.hash(str, max)).toBeLessThan(50);`
`16`	`20`	`});`
`17`	`21`	`test('hash fn throws error if max argument is <= 0', () => {`
`18`	`22`	`let max = 0;`

Lines changed: 5 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -9,7 +9,11 @@ describe('basic hash table', () => {`
`9`	`9`	`});`
`10`	`10`	`test('hash fn takes string and returns number between 0 and specified max', () => {`
`11`	`11`	`const max = 50;`
`12`		`- expect(HT.hash('test', max)).toBeLessThan(50);`
	`12`	`+ let str = '';`
	`13`	`+ for (let i = 0; i < 100; i++) {`
	`14`	`+ str += String.fromCharCode(Math.floor(Math.random() * (200 - 1) + 1));`
	`15`	`+ }`
	`16`	`+ expect(HT.hash(str, max)).toBeLessThan(50);`
`13`	`17`	`});`
`14`	`18`	`test('hash fn throws error if max argument is <= 0', () => {`
`15`	`19`	`let max = 0;`

Lines changed: 21 additions & 6 deletions

Original file line number	Diff line number	Diff line change
`@@ -1,11 +1,26 @@`
`1`		`-class HashTable<T> {`
`2`		`- constructor() {`
`3`		`-`
	`1`	`+class HashTable {`
	`2`	`+ keyMap: [string, string][][];`
	`3`	`+ constructor(size = 83) {`
	`4`	`+ this.keyMap = new Array(size);`
`4`	`5`	`}`
`5`		`- hash = (value: string,max: number): number => {`
	`6`	`+ hash = (key: string): number => {`
`6`	`7`	`// naive hash fn for illustrative purposes`
`7`		`- if (max <= 0) throw TypeError('Max hash value must be a positive integer');`
`8`		`- return value.split('').reduce((a, b) => a * b.charCodeAt(0), 1) % max;`
	`8`	`+ let total = 0;`
	`9`	`+ let prime = 73;`
	`10`	`+ for (let i = 0; i < Math.min(key.length, 100); i++) {`
	`11`	`+ let char = key[i];`
	`12`	`+ let value = char.charCodeAt(0) - 96;`
	`13`	`+ total = (total * prime + value) % this.keyMap.length;`
	`14`	`+ }`
	`15`	`+ return total;`
	`16`	`+ // return value.split('').reduce((a, b) => a * b.charCodeAt(0), 1) % max;`
	`17`	`+ }`
	`18`	`+ set = (key: string, value: string): void => {`
	`19`	`+ let index = this.hash(key);`
	`20`	`+ if (!this.keyMap[index]) {`
	`21`	`+ this.keyMap[index] = [] as [string, string][];`
	`22`	`+ }`
	`23`	`+ this.keyMap[index].push([key, value]);`
`9`	`24`	`}`
`10`	`25`	`}`
`11`	`26`

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