[NWD]prv kolokvium 2018 zadaca 2

const array = [1, 2, [3, 4, [5, 6]]];
function deep_flatten(array){
  return array.reduce(function(flat,toFlatten){
    return flat.concat(Array.isArray(toFlatten)? deep_flatten(toFlatten) : toFlatten);
   },[] )
   }
  console.log(deep_flatten(array));