freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/seek-and-destroy/index.md

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Seek and Destroy

Seek and Destroy

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Problem Explanation

This problem is a bit tricky because you have to familiarize yourself with Arguments, as you will have to work with two or more but on the script you only see two. Many people hardcode this program for three arguments. You will remove any number from the first argument that is the same as any other other arguments.

Relevant Links

• Arguments object
• Array.filter()

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Hints

Hint 1

You need to work with arguments as if it was a regular array. The best way is to convert it into one.

Hint 2

You need to filter, this also means you need to create a callback function. You can use various methods like: indexOf(), includes(). If you need another approach, reduce() might also be of use; keep reading those docs!

Hint 3

To convert arguments into an array use this code var args = Array.prototype.slice.call(arguments);

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Solutions

Solution 1 (Click to Show/Hide)

function destroyer(arr) {
  var args = Array.prototype.slice.call(arguments);

  for (var i = 0; i < arr.length; i++) {
    for (var j = 0; j < args.length; j++) {
      if (arr[i] === args[j]) {
        delete arr[i];
      }
    }
  }
  return arr.filter(Boolean);
}

Code Explanation

1. Create an array of arguments using Array.prototype.slice.call() and store it in the variable args. We'll use this to check against arr.

2. Start a basic for loop to iterate through arr. Nest another for loop inside the first, changing the integer variable j and arr to args. This second loop will iterate through args .

   • Within the second loop create an if statement, checking strictly === that the current val of arr[i] is equal to args[j].

   • If the value at the current index is equal in both arrays, use delete to remove it from arr.

3. Outside of the nested loops: return the modified array using the Boolean object as a filter for any null's created by the delete operator.

Relevant Links

• [arguments
• Array.filter()
• delete
• Boolean

Solution 2 (Click to Show/Hide)

function destroyer(arr) {
  var args = Array.from(arguments).slice(1);
  return arr.filter(function(val) {
    return !args.includes(val);
  });
}

Code Explanation

1. Declare a variable named args and set it equal to a new Array object from() the arguments passed into the function. On the same or next line, use the slice() method on args starting from the second index, 1. This separates the arguments used for filtering into their own array of args.

2. Return the filtered array, using includes() in the callback function to check if val is not in args; returning true to keep the value in the original array or false to remove it.

Relevant Links

• arguments
• Array.slice()
• Array.includes()

Solution 3 (Click to Show/Hide)

const destroyer = (arr, ...args) => arr.filter(i => !args.includes(i));

Code Explanation

• Code using ES6 syntax to declare function using arrow functions.
• Using spread operator to retrieve the arguments.
• Return the filtered array, using includes().

Relevant Links

• Spread Operator