Interleave two arrays (card decks) using recursion... I was able to solve it without recursion but want to know what I am doing wrong

Question

I am attempting to write a function that takes two arrays as inputs, representing the top and bottom halves of a deck of cards, and shuffles them together using recursion. I am attempting return a single array containing the elements from both input arrays interleaved, like so:

• the first element should be the first element of the first input array
• the second element should be the first element of the second input array,
• the third element should be the second element of the first input array,
• the fourth element should be the second element of the second array,

...etc.

I want to append any remaining elements to the end of the array.

This is how I solved it without recursion:

function shuffleCards(topHalf, bottomHalf) {
  let returnArray = [];
  for (let i = 0; i < Math.max(topHalf.length, bottomHalf.length); i++) {
    if (topHalf[i]) {
      returnArray.push(topHalf[i]);
    }
    if (bottomHalf[i]) {
      returnArray.push(bottomHalf[i]);
    }
  }
  return returnArray
}

and this is my attempt with recursion:

function shuffleCards(topHalf, bottomHalf) {
  let results = [];
  if (topHalf.length) {
    results.push(topHalf[0]
    } 
  if (bottomHalf.length) {
      results.push(bottomHalf[0])
    }
  return results.concat(shuffleCards(topHalf.slice(1), bottomHalf.slice(1)));
}

I keep getting the syntax error "missing ) after argument list" but I am fairly certain all of the parenthesis are in the write place.

Any tips?

Thanks!

Answer 1

Beside missing parenthesis, you could take only the first item from the first half and call the function with swapped arrays.

 function shuffleCards([value, ...topHalf], bottomHalf) { return value === undefined ? [] : [value, ...shuffleCards(bottomHalf, topHalf)]; } console.log(...shuffleCards([1, 2, 3, 4], [5, 6, 7, 8]));

Answer 2

function shuffleCards(topHalf, bottomHalf,results = []) {
    if(topHalf.length===0&&bottomHalf.length===0)return results;
    if (topHalf.length!==0) {
    results.push(topHalf[0])
    } 
    if (bottomHalf.length!==0) {
      results.push(bottomHalf[0])
    }
    return shuffleCards(topHalf.slice(1), bottomHalf.slice(1),results);
}