convertFrac.js

/**
 * Description:
 *
 * Common denominators
 *
 * You will have a list of rationals in the form
 *
 * { {numer_1, denom_1} , ... {numer_n, denom_n} }
 * or
 *
 * [ [numer_1, denom_1] , ... [numer_n, denom_n] ]
 * or
 *
 * [ (numer_1, denom_1) , ... (numer_n, denom_n) ]
 * where all numbers are positive ints.
 *
 * You have to produce a result in the form
 *
 * (N_1, D) ... (N_n, D)
 * or
 *
 * [ [N_1, D] ... [N_n, D] ]
 * or
 *
 * [ (N_1', D) , ... (N_n, D) ]
 * or
 *
 * {{N_1, D} ... {N_n, D}}
 * depending on the language (See Example tests)
 *
 * in which D is as small as possible and
 *
 * N_1/D == numer_1/denom_1 ... N_n/D == numer_n,/denom_n.
 * Example:
 *
 * convertFracs [(1, 2), (1, 3), (1, 4)] `shouldBe` [(6, 12), (4, 12), (3, 12)]
 */
function convertFrac(lst) {
    let commonDenom = ((A) => {
        let  a = Math.abs(A[0])

        return A.reduce((prevA, curr) => {
            let b = Math.abs(curr), c = prevA
            while (prevA && b) {
                prevA > b
                    ? prevA %= b
                    : b %= prevA
            }
            return prevA = Math.abs(c*curr) / (prevA+b)
        }, a)
    })(lst.map(el => el[1]))

    return lst.reduce((string, arr) =>
        string += '(' + [commonDenom * arr[0] / arr[1], commonDenom].join(',') + ')', '')
}