add: frequency of alphabet letters

Author: supercodestart

README.md

@@ -4,6 +4,7 @@
 - [Finding all the anagrams](finding-all-the-anagrams)
 - [Finding the maximum depth of a binary tree](finding-the-maximum-depth-of-a-binary-tree)
 - [Fixing setting up a callback](fixing-setting-up-a-callback)
+- [Frequency of alphabet letters](frequency-of-alphabet-letters)
 - [Getting the distinct transactions](getting-the-distinct-transactions)
 - [Replacing characters](replacing-characters)
 - [Replacing with the cipher letters](replacing-with-the-cipher-letters)

frequency-of-alphabet-letters/README.md

@@ -0,0 +1,44 @@
+# Frequency of alphabet letters
+
+In this problem we are asking for implementation in JavaScript of a function, g, that returns the frequency of alphabet letters in a given string ignoring upper/lower case issues.
+
+Use whatever programming language you are most comfortable with, although we prefer to see standard scripting languages used.
+
+The return format is best demonstrated in an example. Suppose you are given the String “Hello there! Apple!" The function g shall return the following structure:
+
+```console
+{
+  a:1,
+  b:0,
+  c:0,
+  d:0,
+  e:4,
+  f:0,
+  g:0,
+  h:2,
+  i:0,
+  j:0,
+  k:0,
+  l:3,
+  m:0,
+  n:0,
+  o:1,
+  p:2,
+  q:0,
+  r:1,
+  s:0,
+  t:1,
+  u:0,
+  v:0,
+  w:0,
+  x:0,
+  y:0,
+  z:0
+}
+```
+
+## Execute
+
+```bash
+node solution.js
+```

frequency-of-alphabet-letters/solution.js

@@ -0,0 +1,21 @@
+function g(str) {
+  const letterFrequencies = {};
+
+  let codeA = 'a'.charCodeAt(0);
+  const codeZ = 'z'.charCodeAt(0);
+
+  while (codeA <= codeZ) {
+    const letter = String.fromCharCode(codeA++);
+
+    letterFrequencies[letter] = str.replace(
+      new RegExp(`[^${letter}]`, 'gi'),
+      '',
+    ).length;
+  }
+
+  return letterFrequencies;
+}
+
+(() => {
+  console.log(g('Hello there! Apple!'));
+})();