LeetCode Notes: Middle of the Linked List

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Questions

Given a non-empty, singly linked list with head node head, return a middle node of linked list.

If there are two middle nodes, return the second middle node.

Example 1:

Input: [1,2,3,4,5]

Output: Node 3 from this list (Serialization: [3,4,5])

The returned node has value 3. (The judge's serialization of this node is [3,4,5]).

Note that we returned a ListNode object ans, such that: ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.

Example 2:

Input: [1,2,3,4,5,6]

Output: Node 4 from this list (Serialization: [4,5,6])

Since the list has two middle nodes with values 3 and 4, we return the second one.

Note:

  • The number of nodes in the given list will be between 1 and 100.

Solution

Analysis:

  1. First serialize the linked list into an array to store the reference of each node
  2. Get the node in the middle of the array

Code:

/**
  * Definition for singly-linked list.
  * function ListNode(val) {
  * this.val = val;
  * this.next = null;
  *}
  */
/**
  * @param {ListNode} head
  * @return {ListNode}
  */
var middleNode = function(head) {
     // Store the reference of each node
     const res = []
     // loop through each node
     while(head){
         // storage node
         const currNode = head
         res.push(currNode)
         head = head.next
     }

     // Take the node in the middle position
     return res[Math.floor(res.length / 2)]
};

Reference

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