create self-describing numbers lesson

curriculum/challenges/english/08-coding-interview-prep/rosetta-code/self-describing-numbers.english.md

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+---
+title: Self-describing numbers
+id: 5eaf48389ee512d4d103684b
+challengeType: 5
+---
+
+## Description
+<section id='description'>
+There are several so-called "self describing" or <a href="https://en.wikipedia.org/wiki/Self-descriptive_number">"self-descriptive"</a> integers. <br />
+
+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 postion is eqal to the number of times that that digit appears in the number. <br />
+
+For example, <b>2020</b> is a four-digit self describing number: <br />
+<ul>
+    <li> position 0 has value 2 and there are two 0s in the number; </li>
+    <li> position 1 has value 0 and there are no 1s in the number; </li>
+    <li> position 2 has value 2 and there are two 2s; </li>
+    <li> position 3 has value 0 and there are zero 3s; </li>
+</ul>
+
+Self-describing numbers < 100.000.000  are:     1210,   2020,   21200,   3211000,   42101000.
+</section>
+
+## Instructions
+<section id='instructions'>
+
+Write a function that will check whether a given positive integer is self-describing.
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+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);
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function isSelfDescribing(n) {
+  // Good luck!
+}
+```
+
+</div>
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+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;
+}
+
+
+```
+
+</section>