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The program has to return a new array of unique values from two original arrays in the order they show up. So there is not sorting required, and there shouldn't be any duplicates.

• JS Arguments

Since you have no idea how many parameters were passed, it would be best to loop through the arguments before looping through the arrays.

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It isn't necessary to use loops. You can use functions such as map(), reduce() or others if you want.

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You will have to check if the current value is already on the array to be returned for every value.

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Solution ahead!

function uniteUnique(arr1, arr2, arr3) {
  // Creates an empty array to store our final result.
  var finalArray = [];

  // Loop through the arguments object to truly made the program work with two or more arrays
  // instead of 3.
  for (var i = 0; i < arguments.length; i++) {
    var arrayArguments = arguments[i];

    // Loops through the array at hand
    for (var j = 0; j < arrayArguments.length; j++) {
      var indexValue = arrayArguments[j];

      // Checks if the value is already on the final array.
      if (finalArray.indexOf(indexValue) < 0) {
        finalArray.push(indexValue);
      }
    }
  }

  return finalArray;
}

// test here
uniteUnique([1, 3, 2], [5, 2, 1, 4], [2, 1]);

🚀 Run Code

• Create empty array finalResult to store the final result.
• Loop through the arguments object in the outer loop and store it in arrayArguments.
• The inner loop is used to loop through individual array elements.
• If the element doesn't already exist in finalArray, add it.
• Return finalArray.

• JS For Loops Explained
• array.length
• JS String Prototype IndexOf
• JS Array Prototype Push

function uniteUnique(arr1, arr2, arr3) {
 var newArr;
 //Convert the arguments object into an array
  var args = Array.prototype.slice.call(arguments);
  //Use reduce function to flatten the array
  newArr = args.reduce(function(arrA,arrB){
  //Apply filter to remove the duplicate elements in the array
    return arrA.concat(arrB.filter(function(i){
      return arrA.indexOf(i) === -1;
    }));
  });

   return newArr;                    
}

// test here
uniteUnique([1, 3, 2], [5, 2, 1, 4], [2, 1]);

🚀 Run Code

• arguments object is converted into an array using slice().
• reduce() function is used to flatten the array i.e., for every element that is in the array (or nested arrays), extract it's elements into one-dimensional array.
• After flattening the array, filter() is used to remove duplicate elements from newArr.

• JS Array Prototype Slice
• JS Array Prototype Reduce
• JS Array Prototype Concat
• JS Array Prototype Filter

function uniteUnique() {
  var concatArr = [];
  var i = 0;
  while (arguments[i]){
    concatArr = concatArr.concat(arguments[i]); i++;
  }
  uniqueArray = concatArr.filter(function(item, pos) {
    return concatArr.indexOf(item) == pos;
  });
  return uniqueArray;
}

// test here
uniteUnique([1, 3, 2], [5, 2, 1, 4], [2, 1]);

🚀 Run Code

• Number of arguments can change dynamically, so we don't need to bother providing our function uniteUnique() with arguments at all.
• We use a while loop to concatenate all the arguments into one array called concatArr.
• We use filter() to remove the duplicate elements by checking the index of each element and removing same elements with different positions.
• Ordering will be preserved here.

• JS While Loop

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Thanks @Rafase282 @sabahang @coded9 for your help with Algorithm: Sorted Union

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