diff --git a/Maths/ExtendedEuclideanGCD.js b/Maths/ExtendedEuclideanGCD.js new file mode 100644 index 000000000..9332aa623 --- /dev/null +++ b/Maths/ExtendedEuclideanGCD.js @@ -0,0 +1,60 @@ +/** + * Problem statement and explanation: https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm + * + * This algorithm plays an important role for modular arithmetic, and by extension for cyptography algorithms + * + * This implementation uses an iterative approach to calculate + */ + +/** + * + * @param {Number} arg1 first argument + * @param {Number} arg2 second argument + * @returns Array with GCD and first and second Bézout coefficients + */ +const extendedEuclideanGCD = (arg1, arg2) => { + if(typeof arg1 != 'number' || typeof arg2 != 'number') throw new TypeError('Not a Number'); + if(arg1 < 1 || arg2 < 1) throw new TypeError('Must be positive numbers'); + + // Make the order of coefficients correct, as the algorithm assumes r0 > r1 + if (arg1 < arg2) { + const res = extendedEuclideanGCD(arg2,arg1) + const temp = res[1] + res[1] = res[2] + res[2] = temp + return res; + } + + // At this point arg1 > arg2 + + // Remainder values + let r0 = arg1 + let r1 = arg2 + + // Coefficient1 values + let s0 = 1 + let s1 = 0 + + // Coefficient 2 values + let t0 = 0 + let t1 = 1 + + while(r1 != 0) { + const q = Math.floor(r0 / r1); + + const r2 = r0 - r1*q; + const s2 = s0 - s1*q; + const t2 = t0 - t1*q; + + r0 = r1 + r1 = r2 + s0 = s1 + s1 = s2 + t0 = t1 + t1 = t2 + } + return [r0,s0,t0]; +} + +export { extendedEuclideanGCD }; +// ex diff --git a/Maths/test/ExtendedEuclideanGCD.test.js b/Maths/test/ExtendedEuclideanGCD.test.js new file mode 100644 index 000000000..0164fac20 --- /dev/null +++ b/Maths/test/ExtendedEuclideanGCD.test.js @@ -0,0 +1,16 @@ +import { extendedEuclideanGCD } from '../ExtendedEuclideanGCD' + +describe('extendedEuclideanGCD', () => { + it('should return valid values in order for positive arguments', () => { + expect(extendedEuclideanGCD(240, 46)).toMatchObject([2, -9, 47]) + expect(extendedEuclideanGCD(46, 240)).toMatchObject([2, 47, -9]) + }) + it('should give error on non-positive arguments', () => { + expect(() => extendedEuclideanGCD(0,240)).toThrowError(new TypeError('Must be positive numbers')) + expect(() => extendedEuclideanGCD(46,-240)).toThrowError(new TypeError('Must be positive numbers')) + }) + it('should give error on non-numeric arguments', () => { + expect(() => extendedEuclideanGCD('240',46)).toThrowError(new TypeError('Not a Number')); + expect(() => extendedEuclideanGCD([240,46])).toThrowError(new TypeError('Not a Number')); + }) +})