What is the difference between [4,null,6] and [4,6]

Question

Here is the question:

Compare two arrays and return a new array with any items only found in one of the two given arrays, but not both. In other words, return the symmetric difference of the two arrays.

And here is my code:

function diffArray(arr1, arr2) {
    var newArr = [];
    // Same, same; but different.
    for (i = 0; i < arr1.length; i++) {
        for (j = 0; j < arr2.length; j++)
            while (arr1[i] === arr2[j])
                delete arr2[j];
        newArr = arr2;
    }
    return newArr;
}

console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));

Please, tell me my mistakes.

Answer 1

If you work using indices as references which you delete, you'll leave those indices undefined. You have to use push to add an item and splice to remove one. The time complexity of the following code should be: O(nm) where n and m are the lengths of the arr1 and arr2 arrays respectively.

function diffArray(arr1, arr2) {
    var newArr = [];
    for (i = 0; i < arr1.length; i++) {
        for (j = 0; j < arr2.length; j++)
            while (arr1[i] === arr2[j])
                arr2.splice(j, 1);
        newArr = arr2;
    }
    return newArr;
}

console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));

This should work, but I've found a different way that is a bit slower for short arrays but much faster for longer array. The time complexity of the following code should be: O(3(n + m)), which is reduced to O(n + m) where n and m are the lengths of the arr1 and arr2 arrays respectively.
Look at this fiddle.
Here's it:

function diffArray(arr1, arr2) {
    let obj1 = {}, obj2 = {};
    for (let l = arr1.length, i = 0; i < l; i++)
        obj1[arr1[i]] = undefined;
    for (let l = arr2.length, i = 0; i < l; i++)
        obj2[arr2[i]] = undefined;
    let a = [];
    for (let arr = arr1.concat(arr2), l = arr.length, i = 0, item = arr[0]; i < l; i++, item = arr[i])
        if (item in obj1 !== item in obj2)
            a.push(item);
    return a;
}

console.log(diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]));