Algorithm Diff Two Arrays

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JS Concepts

JS Language Reference

Explanation:

Check two arrays and return a new array that contains only the items that are not in either of the original arrays.

Hint: 1

Merge the list to make it easy to compare functions.

Hint: 2

Use filter to get the new array, you will need to create a callback function.

Hint: 3

The best way to go about the callback function is to check if the number from the new merged array is not in both original arrays and return it.

Spoiler Alert!

Solution ahead!

Code Solution:

function diff(arr1, arr2) {
  var newArr = arr1.concat(arr2);

  function check(item) {
    if (arr1.indexOf(item) === -1 || arr2.indexOf(item) === -1) {
      return item;
    }
  }

  return newArr.filter(check);
}

Code Solution 2:

function diff(arr1, arr2) {
  // Same, same; but different.
  var newArr = arr1.filter(function (el) {
    return arr2.indexOf(el) === -1;

    // concat the previous output of filter method
    // with the next output of filter method
  }).concat(arr2.filter(function (el) {
    return arr1.indexOf(el) === -1;
  }));
  return newArr;
}

Code Solution 3:

// This solution runs two times faster than solutions 1 and 2
function diff(arr1, arr2) {
  var newArr = [];
  // Looping through arr1 to find elements that do not exist in arr2  
  for (var i = 0; i < arr1.length; i++) {
    if (arr2.indexOf(arr1[i]) === -1){
      // Pushing the unique to arr1 elements to the newArr
      newArr.push(arr1[i]);
    } 
  }
  // Looping through arr2 to find elements that do not exist in arr1
  for (var j = 0; j < arr2.length; j++) {
    if (arr1.indexOf(arr2[j]) === -1){
      // Pushing the unique to arr2 elements to the newArr    
      newArr.push(arr2[j]);
    } 
  }

  return newArr;
}

Credits:

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