[RC Diary] Interviews and exercises (-34)

blog-post.md

[RC Diary] Interviews and exercises (-34)

Soft skills

I've done quite a few interviews today. One of which I don't think went that well, strangely enough it was the first informal interview where I performed badly.

Technical questions

I've got a few questions but the most interesting was the one that I'm about to present, I've changed the wording and everything so that someone googling for the exact woring, fishing for the answer won't get it (no cheating).

Given a function o, it has to respect the following tests: o('.') // gives 'O.' o()('.') // gives 'Oo.' o()()()('!') // gives 'Ooo!' and so on.

My initial approach was this

function o(input) {
  var result = 'O';
  if (input) return result + input;

  function self(input) {
    result += 'o';
    if (input) {
      return result + input;
    } else {
      return self.bind(null);
    }
  }

  return self;
}

Which passed all tests, the next step was the really interesting part:

The function should not have an internal state.

This means that the following should be possible:

var first = o()()()();
var second = o()()();
var third = o();

first('A') + second('B') + third('C'); // OooooAOoooooooBOoooooC

The way I thought about it was that I would've loved the ability to pass around an accumulator, much like things are done when folding over a list to sum its values, the tricky bit in this case is the fact that the accumulator is in the second argument position, so that was the part that took most of the thinking: if you need to be able to accumulate values in the second argument position that you need to do that in a nested function, so I came up with the following implementation.

function o(input, acc) {
  acc = acc || 'O';
  if (input) return acc + input;

  return function(input) {
    return o(input, acc + 'o');
  };
}

where the key part I've been discussing about is this:

return function(input) {
  return o(input, acc + 'o');
};

here I've defined an anonymous function that when applied calls o, with the accumulator in the second position. The need to have acc in the second position derives from the fact that we still need to be able to accept input, so the simplest thing was to just put acc after it.