Find middle element in a linked list

2.20K viewsProgrammingalgorithms element linked-lists middle
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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.
Answered question
0

Simple solution – traversing through the linked list, collecting elements in an array and returning the middle element of the array

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var middleNode = function(head) {
    var arr = [];
    var currNode = head;
         while(currNode) {
        arr.push(currNode)
        currNode = currNode.next;
    }
         var node = (arr.length % 2 === 0) ? arr[arr.length/2] : arr[Math.round(arr.length/2)-1];
         return node;
};

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