Object.keys in reverse order

Question

I have interesting task. I solved the half of it but can't to find the solution to solve the rest. Hope someone can point me to the right direction.

I found the solution close to mine task. But mine is slightly different and use ES6.

There is nested object.

let someList = {

   value: 1,

   next: {

      value: 2,

      next: {

         value: 3,

         next: {

            value: 4,

            next: null

            }

         }

    }

};

I received all values.

function reversePrint(linkedList) {

Object.keys(linkedList).map(key => {
let myKey = linkedList[key];
typeof myKey == "object" ?  console.log(reversePrint(myKey)) : console.log(myKey);
});

}

reversePrint(someList);

But the problem is: how i can get all values in reverse order?

Fiddle: https://jsfiddle.net/L83puqbz/17/

I tried use reduce for to make array and reverse it but every value was in separate array.

Fiddle https://jsfiddle.net/L83puqbz/20/

Any help will be greatly appriciated.

I used but didn't fined a solution with object.keys or reduce — Lucky, Jul 10 '16 at 17:17

curtainrising · Accepted Answer · 2016-07-10T17:31:49.100

5

EDIT - sorry yes, more explanation.

The following code will go through the linked list and print the values in reverse order.

Since the log is after the recursive call, this will go all the way to the last node before the console logs start. Then after each console log, the current function in the stack will end, allowing the previous function to continue to it's print.

let someList = {
  value: 1,
  next: {
    value: 2,
    next: {
      value: 3,
      next: {
        value: 4,
        next: null
      }
    }
  }
};

function printAfter(node){
  if(node.next != null){
    printAfter(node.next);
  }
  console.log(node.value);
}

printAfter(someList)

edited Jul 10 '16 at 17:31

answered Jul 10 '16 at 17:19

curtainrising

249
1
8

Thank you very much for answer! I used recursion and got a numbers but i need to get it in reverse order – Lucky Jul 10 '16 at 17:22
@Lucky so you want `1, 2, 3, 4` as result? Just move the `console.log()` before the if – rpadovani Jul 10 '16 at 17:24
I want 4, 3, 2, 1 as a result – Lucky Jul 10 '16 at 17:25
@Lucky: That's what curtainrising's answer does. It performs the recursion before printing, so the last object found is the first to print out. – Jul 10 '16 at 17:27
The problem is - I need the numbers in reverse order – Lucky Jul 10 '16 at 17:27
@Lucky the code up there prints `4, 3, 2, 1`, so what's the question? – rpadovani Jul 10 '16 at 17:28
Oh, i see! Thank you a lot! – Lucky Jul 10 '16 at 17:29

iaretiga · Answer 2 · 2016-07-10T17:49:11.307

As others have suggested, you can do this with recursion.

function reverse(node) {
    return (node.next === null) ? [node.value] : [...reverse(node.next), node.value];
}

Or, you can use a simple loop:

function reversedValues(node) {
    const values = [];
    while (node !== null) {
        values.unshift(node.value);
        node = node.next;
    }
    return values;
}

Advantage of first solution is simplicity and elegance. Disadvantage is that it can lead to a stack overflow if your linked list is really huge. Second solution is a bit more clunky and verbose, but it's not prone to stack overflow.

Object.keys in reverse order

2 Answers2