Merge-sorted-linked-lists.js

function dll() {
  this.head = null
}

dll.prototype.push = function(val) {
  let head = this.head, curr = head, prev = head
  if (!head) this.head = { val: val, prev: null, next: null }
  else {
    while (curr && curr.next) {
      prev = curr
      curr = curr.next
    }
    curr.next = { val: val, prev: curr, next: null }
  }
}

// output
dll.prototype.print = function() {
  let curr = this.head
  while(curr) {
    console.log(curr.val)
    curr = curr.next
  }
}

// input
let adll = new dll()
adll.push(2)
adll.push(5)
adll.push(7)
adll.push(9)
adll.push(10)

let bdll = new dll()
bdll.push(1)
bdll.push(3)
bdll.push(8)
bdll.push(10)
bdll.push(11)
bdll.push(15)

cdll.print()