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| 1 | +class BloomFilters { |
| 2 | + constructor(size = 101) { |
| 3 | + this.size = size; |
| 4 | + this.data = this.getStorage(size); |
| 5 | + } |
| 6 | + |
| 7 | + add(element) { |
| 8 | + const indices = this.getIndices(element); |
| 9 | + |
| 10 | + for (let i = 0; i < indices.length; i += 1) { |
| 11 | + this.data.setBit(indices[i]); |
| 12 | + } |
| 13 | + } |
| 14 | + |
| 15 | + contains(element) { |
| 16 | + const indices = this.getIndices(element); |
| 17 | + |
| 18 | + for (let i = 0; i < indices.length; i += 1) { |
| 19 | + const index = indices[i]; |
| 20 | + if (!this.data.getBit(index)) { |
| 21 | + return false; // item is definately not there |
| 22 | + } |
| 23 | + } |
| 24 | + return true; // item may be there |
| 25 | + } |
| 26 | + |
| 27 | + getIndices(element) { |
| 28 | + return [this.hashOne(element), this.hashTwo(element), this.hashThree(element)]; |
| 29 | + } |
| 30 | + |
| 31 | + hashOne(value) { |
| 32 | + const stringValue = String(value); |
| 33 | + let hashVal = 0; |
| 34 | + |
| 35 | + for (let i = 0; i < stringValue.length; i += 1) { |
| 36 | + hashVal += stringValue.charCodeAt(i) - 96; |
| 37 | + } |
| 38 | + |
| 39 | + // eslint-disable-next-line no-bitwise |
| 40 | + hashVal &= hashVal; |
| 41 | + |
| 42 | + return Math.abs(hashVal % this.size); |
| 43 | + } |
| 44 | + |
| 45 | + hashTwo(value) { |
| 46 | + const stringValue = String(value); |
| 47 | + const PRIME_MULTIPLIER = 1801; // Random prime number |
| 48 | + let hashVal = 0; |
| 49 | + |
| 50 | + for (let i = 0; i < stringValue.length; i += 1) { |
| 51 | + hashVal += stringValue.charCodeAt(i) - 96; |
| 52 | + hashVal *= PRIME_MULTIPLIER; |
| 53 | + } |
| 54 | + |
| 55 | + return Math.abs(hashVal % this.size); |
| 56 | + } |
| 57 | + |
| 58 | + hashThree(value) { |
| 59 | + const stringValue = String(value); |
| 60 | + const PRIME_MULTIPLIER = 1801; // Random prime number |
| 61 | + const PRIME_ADDER = 2029; // Random prime number |
| 62 | + let hashVal = 0; |
| 63 | + |
| 64 | + for (let i = 0; i < stringValue.length; i += 1) { |
| 65 | + hashVal += stringValue.charCodeAt(i) - 96; |
| 66 | + hashVal *= PRIME_MULTIPLIER; |
| 67 | + hashVal += PRIME_ADDER; |
| 68 | + } |
| 69 | + // eslint-disable-next-line no-bitwise |
| 70 | + hashVal &= hashVal; |
| 71 | + return Math.abs(hashVal % this.size); |
| 72 | + } |
| 73 | + |
| 74 | + // eslint-disable-next-line class-methods-use-this |
| 75 | + getStorage(size) { |
| 76 | + const data = new Array(size).fill(0); |
| 77 | + |
| 78 | + return { |
| 79 | + setBit(index) { |
| 80 | + data[index] = 1; |
| 81 | + }, |
| 82 | + getBit(index) { |
| 83 | + return data[index]; |
| 84 | + }, |
| 85 | + }; |
| 86 | + } |
| 87 | +} |
| 88 | + |
| 89 | +// const b = new BloomFilters(); |
| 90 | + |
| 91 | +// b.add('React.js'); |
| 92 | +// b.add('Node.js'); |
| 93 | + |
| 94 | +// console.log(b.contains('JavaScript')); |
| 95 | +// console.log(b.contains('React.js')); |
| 96 | + |
| 97 | +module.exports = BloomFilters; |
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