TIL of a better way to do the classic Alternating sums test

POSTED ON: Jun 05, 2020

TAGS: javascript basics

This is a common test. Two teams. First value goes into Team 1. Second value goes into Team 2.

So [100, 5, 100, 5, 100, 5] becomes [300, 15];

function alternatingSums(array) {
    let total = [0, 0];
    let isOdd = true;

    for (let i = 0; i < array.length; i++) {
        isOdd ? total[0] += array[i] : total[1] += array[i];
        isOdd = !isOdd;
    }

    return total;
}

This is using a variable true/false to control which direction the values go into.

Another solution is using the % (mod).

function alternatingSums(array) {
    let evenSum = 0;
    let oddSum = 0;

    for(let i = 0; i < array.length; i++) {
        if(i % 2 === 0) {
            evenSum += array[i];
        } else {
            oddSum += array[i];
        }
    }

    return [evenSum, oddSum];
}

TEST SUITE using jasmine:

describe('alternatingSums()', () => {
    it('returns alternating sums of even and odd', () => {
        // arrange
        const nums = [50, 60, 60, 45, 70];

        // act
        const result = alternatingSums(nums);

        // log
        console.log("result: ", result);

        // assert
        expect(result).toEqual([180, 105]);
    });
});

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