Trying to implement isRepdigit() Algorithm in JS

Question

I am pretty new to the Javascript environment. I think one of the most important ways, in order to be good at it, is practice. So I am trying to create a kind of algorithm that detects the number if it has repeated digits.

The algorithm I trying to create should work like below,

Turn the number into a string to use the string prototype.
Use a split prototype to reach each index that number has for the condition.
If arrays first index === arrays[i+1] it should create new array and push(1), else push(0)
At the end of the algorithm we should multiply each element of the last array.
If result return > 0 , "Its True", else "Its False".

Where is my mistake? Anyone can help me?

Here is my code,

function isRepdigit(num) {
  const number = num.toString();
  const newArr = number.split(" ");
  const bag = new Array();
  for (let i = 0; i <= newArr.length; i++) {
    //Number -> 334
    if (newArr[0] === newArr[i]) {
      bag.push(1)
    } else {
      bag.push(0);
    }
  }
  console.log(bag)
  let result = 1;
  for (let i = 0; i < bag.length; i++) {
    result = result * bag[i];
  }
  return result > 0 ? true : false;
}

console.log("1234:", isRepdigit(123))
console.log("1223:", isRepdigit(1223))
console.log("3333:", isRepdigit(3333))

.as-console-wrapper { max-height: 100% !important; }

number.split(" ") won't work, since there are no spaces in number. I think you want number.split(). But you don't need to convert it to an array, you can access characters in a string using number[i] — Barmar
– Barmar, Commented Dec 3, 2020 at 0:07
Why are you only comparing with the first digit? Doesn't 433 have repeated digits? — Barmar
– Barmar, Commented Dec 3, 2020 at 0:09
Are you only trying to detect numbers like 333, 1111, etc.? — Barmar
– Barmar, Commented Dec 3, 2020 at 0:10
It should be false when the number is 455 and it should be true when the number is 555. All the digits have to be the same. — Mustafa Guner
– Mustafa Guner, Commented Dec 3, 2020 at 0:12
You can use a Set to make this much simpler... return (new Set(num.toString())).size === 1 — Phil
– Phil, Commented Dec 3, 2020 at 0:13

Barmar · Accepted Answer · 2020-12-03 16:19:36Z

The problem is your call to num.split(" "). It's splitting the string at space characters, but there are no spaces between the digits. Use num.split("") to turn each character into an array element.

But you don't need to change it to an array, because you can index strings the same way as arrays.

You have another error that's common among beginners: i <= newArray.length needs to use <, not <=.

function isRepdigit(num) {
  const number = num.toString();
  const bag = [];
  for (let i = 0; i < number.length; i++) {
    //Number -> 334
    if (number[0] === number[i]) {
      bag.push(1)
    } else {
      bag.push(0);
    }
  }
  console.log(bag)
  let result = 1;
  for (let i = 0; i < bag.length; i++) {
    result = result * bag[i];
  }
  return result > 0 ? true : false;
}

console.log("1234:", isRepdigit(123))
console.log("1223:", isRepdigit(1223))
console.log("3333:", isRepdigit(3333))

.as-console-wrapper { max-height: 100% !important; }

But your entire algorithm is poor. There's no need to make an array of all the comparisons. You can simply return false as soon as you find a character that doesn't match.

function isRepdigit(num) {
  const number = num.toString();
  for (let i = 1; i < number.length; i++) {
    if (number[0] !== number[i]) {
      return false;
    }
  }
  return true;
}

console.log("1234:", isRepdigit(123))
console.log("1223:", isRepdigit(1223))
console.log("3333:", isRepdigit(3333))

.as-console-wrapper {
  max-height: 100% !important;
}

See also Function that checks whether all characters in a string are equal javascript - Homework Warning

aleEspinosaM · Accepted Answer · 2020-12-03 17:06:46Z

1

you could use a Set in javascript,

The Set object lets you store unique values of any type, whether primitive values or object references.

function isRepDigit(num) {
    const strNum = num.toString();
    return [...new Set(strNum)].length !== [...strNum].length
}

and because a set will return uniq values, you could compare the lengths between the number provided and the set

answered Dec 3, 2020 at 17:06

aleEspinosaM

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