This was an interesting challenge that involves converting a multi-digit number to an array, then using array methods, the spread operator and the new Set constructor to determine if the array contains all of the digits 0-9.

A setin JavaScript is a collection of unique values. If you were to have an array of numbers, for example [1,2,3,4,4,5,6], it would not be considered a set unless the extra 4 were removed.

There’s a way we can remove extra repeated values using the new Set constructor. Here’s an example:

const array = [1,2,3,4,4,5,6]

new Set(array);
// Set(6) {
  1,
  2,
  3,
  4,
  5,
  6,
  __proto__: { // some methods in here  }
}

So, if we use the new Set constructor to create a set from the array, then we get an array that just has one of each unique value - in this case just one of each number. The extra four is removed.

Now, we can take this knowledge and a little know how of JavaScript and array methods and use it to solve this problem.

Pandigital numbers

A pandigital number contains all digits (0-9) at least once. Write a function that takes an integer, returning true if the integer is pandigital, and false otherwise.

Examples

isPandigital(98140723568910) ➞ true

isPandigital(90864523148909) ➞ false // 7 is missing.

isPandigital(112233445566778899) ➞ false // 0 is missing

One approach:

const num1 = 84847473937
const num2 = 546732965015
const num3 = 6781235184590
const num4 = 9432821089765
const num5 = 629764
const num6 = 90864523148909

function isPandigital(num) {
  // convert the number to a string, separate all the numbers in an array, 
  // convert each to a number then sort them in ascending order
  const numbers = [...String(num)].map( x => +x).sort((p,c) => p-c)
  // take the array of numbers from above and  remove the repeated values, 
  // then join them togeher to make a string.  
  // Check to see if the string contains all of the digits 0-9
  return [...new Set(numbers)].join('') === '0123456789' 
}

isPandigital(num1) //false
isPandigital(num2) //false
isPandigital(num3) //true
isPandigital(num4) //true
isPandigital(num5) //false
isPandigital(num6) //false

Our solution above is pretty straightforward, once you know what’s going on. First, we convert the number to a string, then we use one of the handy uses of the the spread operator to separate all the digits into an array. After than, we use map to convert each stringified number from a string back to an number by applying the unary opertator.

Then we use the sort method to sort the array in ascending order by passing in a subtraction function to the method.

The new Set constructor is a handy way to remove repeated values as shown above and here we put it to use by passing the numbers array into it. This gives us an array that only has one of each unique value.

Finally, we use the join method to join the array of numbers into a string. We then check to see if the string contains all of the digits 0-9 by comparing it with the string '0123456789'. If it does, then we return true, otherwise we return false.

Here are some other solutions written by others that are more concise.

This solution uses applies the new Set constructor to the converted number which is then split. Lastly, it checks to see if the size is equal to 10. Since the new Set constructor removes repeated values, the size of the array will be 10 if the number is pandigital.

function isPandigital(num) {
	return new Set(num.toString().split('')).size===10
}

This solution uses regex to determine if all numbers 0-9 are included individually. new Set is not used since regex is used for finding the individual digits.

function isPandigital(num) {
	var a = (''+num).split('').sort((a,b)=>a-b).join('');
	return /^0+1+2+3+4+5+6+7+8+9+$/.test(a);
}

This solution is the most concise, and makes use of new Set.

const isPandigital = n => new Set(n+'').size > 9