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added-ModularArithmetic-code#1217

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56 changes: 56 additions & 0 deletionsMaths/ModularArithmetic.js
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import { extendedEuclideanGCD } from './ExtendedEuclideanGCD'

/**
* https://brilliant.org/wiki/modular-arithmetic/
* @param {Number} arg1 first argument
* @param {Number} arg2 second argument
* @returns {Number}
*/

export class ModRing {
constructor (MOD) {
this.MOD = MOD
}

isInputValid = (arg1, arg2) => {
if (!this.MOD) {
throw new Error('Modulus must be initialized in the object constructor')
}
if (typeof arg1 !== 'number' || typeof arg2 !== 'number') {
throw new TypeError('Input must be Numbers')
}
}
/**
* Modulus is Distributive property,
* As a result, we separate it into numbers in order to keep it within MOD's range
*/

add = (arg1, arg2) => {
this.isInputValid(arg1, arg2)
return ((arg1 % this.MOD) + (arg2 % this.MOD)) % this.MOD
}

subtract = (arg1, arg2) => {
this.isInputValid(arg1, arg2)
// An extra MOD is added to check negative results
return ((arg1 % this.MOD) - (arg2 % this.MOD) + this.MOD) % this.MOD
}

multiply = (arg1, arg2) => {
this.isInputValid(arg1, arg2)
return ((arg1 % this.MOD) * (arg2 % this.MOD)) % this.MOD
}

/**
*
* It is not Possible to find Division directly like the above methods,
* So we have to use the Extended Euclidean Theorem for finding Multiplicative Inverse
* https://github.com/TheAlgorithms/JavaScript/blob/master/Maths/ExtendedEuclideanGCD.js
*/

divide = (arg1, arg2) => {
// 1st Index contains the required result
// The theorem may have return Negative value, we need to add MOD to make it Positive
return (extendedEuclideanGCD(arg1, arg2)[1] + this.MOD) % this.MOD
}
}
45 changes: 45 additions & 0 deletionsMaths/test/ModularArithmetic.test.js
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import { ModRing } from '../ModularArithmetic'

describe('Modular Arithmetic', () => {
const MOD = 10000007
let ring
beforeEach(() => {
ring = new ModRing(MOD)
})

describe('add', () => {
it('Should return 9999993 for 10000000 and 10000000', () => {
expect(ring.add(10000000, 10000000)).toBe(9999993)
})
it('Should return 9999986 for 10000000 and 20000000', () => {
expect(ring.add(10000000, 20000000)).toBe(9999986)
})
})

describe('subtract', () => {
it('Should return 1000000 for 10000000 and 9000000', () => {
expect(ring.subtract(10000000, 9000000)).toBe(1000000)
})
it('Should return 7 for 10000000 and 20000000', () => {
expect(ring.subtract(10000000, 20000000)).toBe(7)
})
})

describe('multiply', () => {
it('Should return 1000000 for 100000 and 10000', () => {
expect(ring.multiply(100000, 10000)).toBe(9999307)
})
it('Should return 7 for 100000 and 10000100', () => {
expect(ring.multiply(10000000, 20000000)).toBe(98)
})
})

describe('divide', () => {
it('Should return 4 for 3 and 11', () => {
expect(ring.divide(3, 11)).toBe(4)
})
it('Should return 2 for 18 and 7', () => {
expect(ring.divide(18, 7)).toBe(2)
})
})
})

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