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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/gray-code.md

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+---
+title: Gray code
+id: 5a23c84252665b21eecc7e80
+challengeType: 5
+forumTopicId: 302276
+---
+
+## Description
+<section id='description'>
+<a href="https://en.wikipedia.org/wiki/Gray code" target="_blank">Gray code</a> is a form of binary encoding where transitions between consecutive numbers differ by only one bit.
+This is a useful encoding for reducing hardware data hazards with values that change rapidly and/or connect to slower hardware as inputs.
+It is also useful for generating inputs for <a href="https://en.wikipedia.org/wiki/Karnaugh map" target="_blank">Karnaugh maps</a> in order from left to right or top to bottom.
+</section>
+
+## Instructions
+<section id='instructions'>
+Create a function to encode a number to and decode a number from Gray code. The function should will have 2 parameters.
+The first would be a boolean. The function should encode for true and decode for false. The second parameter would be the number to be encoded/decoded.
+Display the normal binary representations, Gray code representations, and decoded Gray code values for all 5-bit binary numbers (0-31 inclusive, leading 0's not necessary).
+There are many possible Gray codes. The following encodes what is called "binary reflected Gray code."
+Encoding (MSB is bit 0, b is binary, g is Gray code):
+<pre>
+if b[i-1] = 1
+  g[i] = not b[i]
+else
+  g[i] = b[i]
+</pre>
+Or:
+<pre>
+g = b xor (b logically right shifted 1 time)
+</pre>
+Decoding (MSB is bit 0, b is binary, g is Gray code):
+<pre>
+b[0] = g[0]<br>
+for other bits:
+b[i] = g[i] xor b[i-1]
+</pre>
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>gray</code> should be a function.
+    testString: assert(typeof gray=='function');
+  - text: <code>gray(true,177)</code> should return a number.
+    testString: assert(typeof gray(true,177)=='number');
+  - text: <code>gray(true,177)</code> should return <code>233</code>.
+    testString: assert.equal(gray(true,177),233);
+  - text: <code>gray(true,425)</code> should return <code>381</code>.
+    testString: assert.equal(gray(true,425),381);
+  - text: <code>gray(true,870)</code> should return <code>725</code>.
+    testString: assert.equal(gray(true,870),725);
+  - text: <code>gray(false,233)</code> should return <code>177</code>.
+    testString: assert.equal(gray(false,233),177);
+  - text: <code>gray(false,381)</code> should return <code>425</code>.
+    testString: assert.equal(gray(false,381),425);
+  - text: <code>gray(false,725)</code> should return <code>870</code>.
+    testString: assert.equal(gray(false,725),870);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function gray(enc, number) {
+
+}
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function gray(enc, number){
+  if(enc){
+      return number ^ (number >> 1);
+  }else{
+      let n = number;
+
+      while (number >>= 1) {
+          n ^= number;
+      }
+      return n;
+  }
+}
+
+```
+
+</section>