Double Linked List.ipynb

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   "source": [
    "class Node:\n",
    "    def __init__(self,data):\n",
    "        self.data = data\n",
    "        self.next = None\n",
    "        self.prev = None\n",
    "    \n",
    "class DoubleLinkedList:\n",
    "    def __init__(self):\n",
    "        self.head = None\n",
    "    \n",
    "    def append(self,data):\n",
    "        if self.head is None:\n",
    "            new_node = Node(data)\n",
    "            new_node.prev = None\n",
    "            self.head = new_node\n",
    "        else:\n",
    "            new_node = Node(data)\n",
    "            cur = self.head\n",
    "            while cur.next:\n",
    "                cur = cur.next\n",
    "            cur.next = new_node\n",
    "            new_node.prev = cur\n",
    "            new_node.next = None\n",
    "    \n",
    "    def prepend(self,data):\n",
    "        if self.head is None:\n",
    "            new_node = Node(data)\n",
    "            new_node.prev = None\n",
    "            self.head = new_node\n",
    "        else:\n",
    "            new_node = Node(data)\n",
    "            self.head.prev = new_node\n",
    "            new_node.next = self.head\n",
    "            new_node.prev = None\n",
    "            self.head = new_node\n",
    "    \n",
    "    def add_after_node(self,key,data):\n",
    "        cur = self.head\n",
    "        while cur:\n",
    "            if cur.next is None and cur.data == key:\n",
    "                self.append(data)\n",
    "                break\n",
    "            elif cur.data == key:\n",
    "                new_node = Node(data)\n",
    "                nxt = cur.next\n",
    "                cur.next = new_node\n",
    "                new_node.next = nxt\n",
    "                new_node.prev = cur\n",
    "                nxt.prev = new_node\n",
    "            cur = cur.next\n",
    "            \n",
    "    def add_before_node(self,key,data):\n",
    "        cur = self.head\n",
    "        while cur:\n",
    "            if cur.prev is None and cur.data == key:\n",
    "                self.prepend(data)\n",
    "                break\n",
    "            elif cur.data == key:\n",
    "                new_node = Node(data)\n",
    "                prev = cur.prev\n",
    "                prev.next = new_node\n",
    "                new_node.next = cur\n",
    "                new_node.prev = prev\n",
    "                cur.prev = new_node\n",
    "            cur = cur.next\n",
    "    \n",
    "    def delete_node(self,data):\n",
    "        cur = self.head\n",
    "        while cur:\n",
    "            if cur.data == data and cur.prev is None and cur.next is None:\n",
    "                if not cur.next:\n",
    "                    cur = None\n",
    "                    self.head = None\n",
    "                    break\n",
    "        \n",
    "                elif cur.prev is None:\n",
    "                    nxt = cur.next \n",
    "                    cur = None\n",
    "                    nxt.prev = None\n",
    "                    self.head = nxt\n",
    "                    break\n",
    "            elif cur.data == data:\n",
    "                if cur.next:\n",
    "                    nxt = cur.next\n",
    "                    prev = cur.prev\n",
    "                    cur = None\n",
    "                    prev.next = nxt\n",
    "                    nxt.prev = prev\n",
    "                    break\n",
    "                else:\n",
    "                    prev = cur.prev\n",
    "                    prev.next = None\n",
    "                    cur = None\n",
    "                    break\n",
    "                \n",
    "            cur = cur.next\n",
    "    \n",
    "    def reverse(self):\n",
    "        tmp = None\n",
    "        cur = self.head\n",
    "        while cur:\n",
    "            tmp = cur.prev\n",
    "            cur.prev = cur.next\n",
    "            cur.next = tmp\n",
    "            cur = cur.prev\n",
    "        self.head = tmp.prev\n",
    "            \n",
    "    def print_list(self):\n",
    "        cur = self.head\n",
    "        while cur:\n",
    "            print(cur.data)\n",
    "            cur = cur.next\n",
    "    "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 79,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2\n",
      "1\n",
      "2\n",
      "3\n",
      "4\n"
     ]
    }
   ],
   "source": [
    "dlist = DoubleLinkedList()\n",
    "dlist.append(1)\n",
    "dlist.append(2)\n",
    "dlist.append(3)\n",
    "dlist.append(4)\n",
    "dlist.reverse()\n",
    "dlist.print_list()"
   ]
  }
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