fix: replace .english.md extension with .md

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

@@ -0,0 +1,136 @@
+---
+title: Ethiopian multiplication
+id: 599d1566a02b571412643b84
+challengeType: 5
+forumTopicId: 302257
+---
+
+## Description
+<section id='description'>
+Ethiopian multiplication is a method of multiplying integers using only addition, doubling, and halving.
+<strong>Method:</strong>
+<ol>
+  <li>Take two numbers to be multiplied and write them down at the top of two columns</li>
+  <li>In the left-hand column repeatedly halve the last number, discarding any remainders, and write the result below the last in the same column, until you write a value of <code>1</code></li>
+  <li>In the right-hand column repeatedly double the last number and write the result below. stop when you add a result in the same row as where the left hand column shows <code>1</code></li>
+  <li>Examine the table produced and discard any row where the value in the left column is even</li>
+  <li>Sum the values in the right-hand column that remain to produce the result of multiplying the original two numbers together</li>
+</ol>
+<strong>For example:</strong> <code>17 &times; 34</code>
+<pre>
+17   34
+</pre>
+Halving the first column:
+<pre>
+17   34
+8
+4
+2
+1
+</pre>
+Doubling the second column:
+<pre>
+17   34
+8    68
+4   136
+2   272
+1   544
+</pre>
+Strike-out rows whose first cell is even:
+<pre>
+17   34
+8    <strike>68</strike>
+4   <strike>136</strike>
+2   <strike>272</strike>
+1   544
+</pre>
+Sum the remaining numbers in the right-hand column:
+<pre>
+17   34
+8    --
+4   ---
+2   ---
+1   544
+   ====
+    578
+</pre>
+So <code>17</code> multiplied by <code>34</code>, by the Ethiopian method is <code>578</code>.
+</section>
+
+## Instructions
+<section id='instructions'>
+The task is to define three named functions/methods/procedures/subroutines:
+<ol>
+  <li>one to halve an integer,</li>
+  <li>one to double an integer, and</li>
+  <li>one to state if an integer is even</li>
+</ol>
+Use these functions to create a function that does Ethiopian multiplication.
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>eth_mult</code> should be a function.
+    testString: assert(typeof eth_mult === 'function');
+  - text: <code>eth_mult(17,34)</code> should return <code>578</code>.
+    testString: assert.equal(eth_mult(17, 34), 578);
+  - text: <code>eth_mult(23,46)</code> should return <code>1058</code>.
+    testString: assert.equal(eth_mult(23, 46), 1058);
+  - text: <code>eth_mult(12,27)</code> should return <code>324</code>.
+    testString: assert.equal(eth_mult(12, 27), 324);
+  - text: <code>eth_mult(56,98)</code> should return <code>5488</code>.
+    testString: assert.equal(eth_mult(56, 98), 5488);
+  - text: <code>eth_mult(63,74)</code> should return <code>4662</code>.
+    testString: assert.equal(eth_mult(63, 74), 4662);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function eth_mult(a, b) {
+
+}
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function eth_mult(a, b) {
+  let sum = 0; a = [a]; b = [b];
+
+  let half = a => a / 2,
+    double = a => a * 2,
+    is_even = a => a % 2 == 0;
+
+  while (a[0] !== 1) {
+    a.unshift(Math.floor(half(a[0])));
+    b.unshift(double(b[0]));
+  }
+
+  for (let i = a.length - 1; i > 0; i -= 1) {
+    if (!is_even(a[i])) {
+      sum += b[i];
+    }
+  }
+  return sum + b[0];
+}
+```
+
+</section>