Coding challenge #2 - Winners!

armandocat(63)

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Last week I posted my second contest with a coding problem to solve.
Now it's time to acknowledge and reward the winners!

Contest #2

In a Linked list, each node has a value and a next node.
Given a Linked list:

Write a function that reverse the linked list, using a recursive algorithm.
Write a function that reverse the linked list, using a iterative algorithm.
- For instance: given A -> B -> C it returns C -> B ->A

You don't have to clone the nodes, you must just work on their next properties.

The preferred language to use this time is javascript, but you can also use other languages as well. You will need to translate the starting code to the language of your choice.

Winners

There were 5 participants and all of them solved the problems well!
Perhaps the problem was easier than I thought! I’ll try and make the next ones harder!

As promised, the rewards will be based on clarity of the code and the time of submission.

Hope to see your solutions to my future contests too!

Best solution

function reverseRecursive(obj) {
  var next = obj && obj.next;
  if(!next){
    return obj;
  }
  var reversedTail = reverseRecursive(next);
  obj.next = null;
  next.next = obj;
  return reversedTail;
}

function reverseIterative(obj) {
  var reversed;
  while(obj){
    var next = obj.next;
    obj.next = reversed;
    reversed = obj;
    obj = next;
  }
  return reversed;
}


/***************************/
/***************************/
/* DO NOT CHANGE DOWN HERE */
/***************************/
/***************************/


function Obj(v, next) {
  this.v = v;
  this.next = next;
}
Obj.prototype.toString = function() {
  var next = this.next ? ' -> ' + this.next.toString() : '';
  return this.v + next;
};
Obj.prototype.clone = function() {
  return new Obj(this.v, this.next && this.next.clone());
};

function arrayToObj(array) {
  var obj;
  for (var i = array.length - 1; i >= 0; i--) {
    obj = new Obj(array[i], obj);
  }  
  return obj;
}



function test(array) {
  var obj = arrayToObj(array);
  console.log('Original:')
  console.log(obj && obj.toString());

  var r1 = reverseRecursive(obj && obj.clone());
  console.log('Reversed (recursive algorithm):');
  console.log(r1 && r1.toString());

  var r2 = reverseIterative(obj && obj.clone());
  console.log('Reversed (iterative algorithm):');
  console.log(r2 && r2.toString());

  console.log();
}

test([1, 2, 3, 4, 5, 6]);
test([1]);
test([]);