{
 "cells": [
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   "cell_type": "markdown",
   "source": [
    "Given a non-empty, singly linked list with head node `head`, return a middle\n",
    "node of linked list.\n",
    "\n",
    "If there are two middle nodes, return the second middle node.\n",
    "\n",
    "\n",
    "\n",
    "**Example 1:**\n",
    "\n",
    "\n",
    "\n",
    "    Input: [1,2,3,4,5]\n",
    "    Output: Node 3 from this list (Serialization: [3,4,5])\n",
    "    The returned node has value 3.  (The judge's serialization of this node is [3,4,5]).\n",
    "    Note that we returned a ListNode object ans, such that:\n",
    "    ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.\n",
    "\n",
    "\n",
    "**Example 2:**\n",
    "\n",
    "\n",
    "\n",
    "    Input: [1,2,3,4,5,6]\n",
    "    Output: Node 4 from this list (Serialization: [4,5,6])\n",
    "    Since the list has two middle nodes with values 3 and 4, we return the second one.\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Note:**\n",
    "\n",
    "  * The number of nodes in the given list will be between `1` and `100`."
   ],
   "metadata": {}
  },
  {
   "outputs": [
    {
     "output_type": "execute_result",
     "data": {
      "text/plain": "middle_node_by_double_pointers (generic function with 1 method)"
     },
     "metadata": {},
     "execution_count": 1
    }
   ],
   "cell_type": "code",
   "source": [
    "# @lc code=start\n",
    "using LeetCode\n",
    "\n",
    "# double pointers\n",
    "function middle_node_by_double_pointers(head::ListNode)::ListNode\n",
    "    p1 = p2 = head\n",
    "    while !isnothing(p2)\n",
    "        p2 = next(p2)\n",
    "        isnothing(p2) && return p1\n",
    "        p2, p1 = p2.next, p1.next\n",
    "    end\n",
    "    return p1\n",
    "end\n",
    "\n",
    "# @lc code=end"
   ],
   "metadata": {},
   "execution_count": 1
  },
  {
   "cell_type": "markdown",
   "source": [
    "---\n",
    "\n",
    "*This notebook was generated using [Literate.jl](https://github.com/fredrikekre/Literate.jl).*"
   ],
   "metadata": {}
  }
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