Work on your ability to communicate?

Your example as you have literally explained it entails just deleting all repeats (ambiguous if 121 -> 12 or 121, or for that matter if 121 is possible as an input). Either way a simple for loop could solve it. But you are a self proclaimed smart person who eats for loops for breakfast, so it seems your have over simplified your description of the problem.

Machine learning is essentially the following:

• For sets X and Y, take a collection of some functions F = {f: X -> Y}
• Take a probability distribution D on X x Y. Note this could be of the form (x, g(x)) for fixed unknown function g where only x is random.
• Take a loss function L: F -> R, eg L(f) = ExpectedValue( distance(f(x),y) )
• Sample data from the distribution
• ???
• Have an f in F that is close to minimizing L

So tell us what F, X, Y, D, L are.

I thought software engineers were "professional googlers"?

Your description of the problem makes it sounds very similar to autocorrect. Maybe learn how that is done and adapt it?

No one is actually going to be of any help unless you more precisely phrase your problem.