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title	id	challengeType	forumTopicId
Self Describing Numbers	5eaf48389ee512d4d103684b	5	385289

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.

Tests

tests:
  - text: <code>isSelfDescribing</code> should be a function.
    testString: assert(typeof isSelfDescribing=='function');
  - text: <code>isSelfDescribing()</code> should return a boolean.
    testString: assert(typeof isSelfDescribing(2020) =='boolean');
  - text: <code>isSelfDescribing(2020)</code> should return <code>true</code>.
    testString: assert.equal(isSelfDescribing(2020), true);
  - text: <code>isSelfDescribing(3021)</code> should return <code>false</code>.
    testString: assert.equal(isSelfDescribing(3021), false);
  - text: <code>isSelfDescribing(3211000)</code> should return <code>true</code>.
    testString: assert.equal(isSelfDescribing(3211000), true);

Challenge Seed

function isSelfDescribing(n) {

}

Solution

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;
}

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