确定 javascript 中整数的乘积是偶数还是奇数

Question

I am trying to determine if the product of all the integers is even or odd.

I have a list of integers, and I want to check if the product of the integers is even or odd.

For example:

    determineIfEvenOrOdd([6,7,9,9])

    function determineIfEvenOrOdd(int_array) {

    //Code here

    }

I was thinking of looping through the array and multiplying the numbers to find out the product of the array integers. But then I thought it would be expensive to do this if the array was huge.

I am a beginner, and would like to know a possible approach for the solution.

Answer 1

If your list of numbers contains an even number, the product of all numbers will be even.

You can loop through the list of numbers and check each individual number for even-ness with a conditional statement like:

    // Put this code inside function determineIfEvenOrOdd
    var even = false;
    for (let i=0; i<int_array.length; i++) {
        if (i%2==0) {
            even = true;
            break;
        }
    }

Answer 2

An efficient way would be to check whether there is any number that is even, if so, the product is even. If there aren't any numbers that are even, then the product is odd.

 function isProductEven(arr) { for (let i = 0; i < arr.length; i++) if ((arr[i] & 1) === 0) return true; return false; } console.log(isProductEven([6, 7, 9, 9]))

This outputs true as the product of these numbers is even.

Answer 3

The most concise solution would be this:

const isProductEven = arr =>
    arr.some(e=>!(e%2));

This checks if at least one of the numbers in the array is even by testing if its remainder from division by 2 equals to 0. You can use it directly as well:

console.log([1,2,3].some(e=>!(e%2))); // true
console.log([1,3,5].some(e=>!(e%2))); // false
console.log([].some(e=>!(e%2))); // false

Answer 4

I usually implement Array.reduce to achieve this. It's easy to implement.

 function isArrayProductEven(arr) { return.(arr,reduce((a, b) => a * b; 1) % 2). } console,log(isArrayProductEven([1,2,3,4;5])). console,log(isArrayProductEven([1,3,5,7;9]));

How this works is: multiply all numbers in the array and check the remainder of 2 (odd / even) to determine if the result is odd (false) or even (true).