freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/rosetta-code/self-describing-numbers.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5eaf48389ee512d4d103684b	Self Describing Numbers	5	385289	self-describing-numbers

--description--

There are several so-called "self describing" or "self-descriptive" integers.

An integer is said to be "self-describing" if it has the property that, when digit positions are labeled 0 to N-1, the digit in each position is equal to the number of times that digit appears in the number.

For example, 2020 is a four-digit self describing number:

• position 0 has value 2 and there are two 0s in the number;
• position 1 has value 0 and there are no 1s in the number;
• position 2 has value 2 and there are two 2s;
• position 3 has value 0 and there are zero 3s;

Self-describing numbers < 100,000,000 are: 1210, 2020, 21200, 3211000, 42101000.

--instructions--

Write a function that takes a positive integer as a parameter. If it is self-describing return true. Otherwise, return false.

--hints--

isSelfDescribing should be a function.

assert(typeof isSelfDescribing == 'function');

isSelfDescribing() should return a boolean.

assert(typeof isSelfDescribing(2020) == 'boolean');

isSelfDescribing(2020) should return true.

assert.equal(isSelfDescribing(2020), true);

isSelfDescribing(3021) should return false.

assert.equal(isSelfDescribing(3021), false);

isSelfDescribing(3211000) should return true.

assert.equal(isSelfDescribing(3211000), true);

--seed--

--seed-contents--

function isSelfDescribing(n) {

}

--solutions--

function isSelfDescribing(n) {
    let digits = String(n).split("");
    digits = digits.map(function(e) {return parseInt(e)});
    let count = digits.map((x) => {return 0})
    digits.forEach((d) =>{
        if (d >= count.length) {
            return false
        }
        count[d] += 1;
    });

     if (digits === count) {
        return true;
    }
    if (digits.length != count.length) {
        return false;
    }
    
    for (let i=0; i< digits.length; i++){
      if (digits[i] !== count[i]) {
        return false;
      }
    }
    return true;
}