<pre class="shiki github-dark shaku"><code>type Alphabet = {"A":'a',"B":'b',"C":'c',"D":'d',"E":'e',"F":'f',"G":'g',"H":'h',"I":'i',"J":'j',"K":'k',"L":'l',"M":'m',"N":'n',"O":'o',"P":'p',"Q":'q',"R":'r',"S":'s',"T":'t',"U":'u',"V":'v',"W":'w',"X":'x',"Y":'y',"Z":'z'}type SnakeCase&lt;S extends string,A extends string='', Index extends any[]=[]&gt; = S extends `${infer F}${infer L}`? F extends keyof Alphabet? Index[`length`] extends 0? SnakeCase&lt;L,`${A}${Alphabet[F]}`,[...Index,0]&gt;: SnakeCase&lt;L,`${A}_${Alphabet[F]}`,[...Index,0]&gt; : SnakeCase&lt;L,`${A}${F}`,[...Index,0]&gt;:A// your code here</code></pre>

This is my accepted solution

Implement SnakeCase<S> to turn string in camel case to snake case. type A = SnakeCase<'BigFrontEnd'> // big_front_end…