876. Middle of the Linked List

Problem

Tags: Linked List, Two Pointers

Given the head of a singly linked list, return the middle node of the linked list.

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

Example 1:

Input: head = [1,2,3,4,5]
Output: [3,4,5]
Explanation: The middle node of the list is node 3.

Example 2:

Input: head = [1,2,3,4,5,6]
Output: [4,5,6]
Explanation: Since the list has two middle nodes with values 3 and 4, we return the second one.

Constraints:

• The number of nodes in the list is in the range [1, 100].
• 1 <= Node.val <= 100

Code

C

// 876. Middle of the Linked List (11/25/54210)
// Runtime: 0 ms (94.37%) Memory: 5.75 MB (75.42%) 

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */


struct ListNode* middleNode (struct ListNode* head) {
    int i = 0;
    struct ListNode* middle = head;
    
    while (head) {
        if (i % 2) {
            middle = middle->next;
        }
        i++;
        head = head->next;
    }
    
    return middle;
}

JS

// 876. Middle of the Linked List (4/18/53723)
// Runtime: 76 ms (46.99%) Memory: 38.98 MB (92.21%) 

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
function middleNode(head) {
    let middle = head, tail = head;
    for(let i = 1; true; i++) {
        if(tail.next) {
            tail = tail.next;
            if(i % 2) middle = middle.next;
        } else break;
    }
    return middle;
};