Algorithm Help Diff Array

JavaScript
1

I’m wondering why my arr4 does not contain unique elements from 1 array.

  **Your code so far**


function diffArray(arr1, arr2) {
let arr3 = arr1.concat(arr2);
let count = 0;
let arr4 = [];
//count numbers if they are 1 then add them to a new arr called arr4
for (let i = 0;   i < arr3.length; i++) {
  for (let j = 0; j < arr3.length; j++) {
    if (arr3[i] === arr3[j]) {
      count++
    }
  }
  }
if (count === 1) {
   arr4.concat(arr3[j])
}
return arr4;
}

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

  **Your browser information:**

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 11_2_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.90 Safari/537.36.

Challenge: Diff Two Arrays

Link to the challenge:

2

Could you explain how it’s supposed to work? Maybe with some example?

3

It’s supposed to count the unique elements in the combined array then when the count is 1 append those numbers to a new array called arr4, but when I return arr4 it does not seem to return anything, when in fact it’s supposed to return [4]. I might have to use another data structure to do a count like a dictionary.

4

Take a look what’s the value of count before the it’s checked if it’s 1.

5

the count prints the numbers 1 to 17.

6

With the code from original post it should be only 17. Are you able to figure out why that’s happening?

7

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