linkedList.js

//flat an array
function flat(arr, depth) {
  if (depth > 0) {
    return arr.reduce(
      (acc, val) => acc.concat(Array.isArray(val) ? flat(val, depth - 1) : val),
      []
    )
  } else {
    return arr.slice()
  }
}
let arr1 = [1, [2, 3], [3, [4, 5]], 4, 5]

// console.log(flat(arr1, 'infinity'))
console.log(flat(arr1, 2))


//find the sise of a linked list
 sise() {
   this.count = 0
   let current = this.head
   while(current) {
     this.count++
     current = current.next
   }
   return this.count
  }

 deleteTail() {
    if (this.head === this.tail) {
      this.head = this.tail = null
    } else {
      this.tail = this.tail.prev
      this.tail.next = null
    }
   
    insertBefore(val, existing) {
    let current = this.head
    while (current){
      if (current.value === existing) {
        break;
      }
      current = current.next
    }

    let newNode = new Node(val)
    let prevNode = current.prev
    prevNode.next = newNode
    newNode.next = current
  }
  }