876. Middle of the Linked List

Middle of the Linked List

Problem Description

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

Approach) Slow - Fast Pointer

/**
 * 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}
 */
var middleNode = function(head) {
    let fast = head;
    let slow = head;

    while (fast != null && fast.next != null ) {
      fast = fast.next.next;
      slow = slow.next;
    }
    return slow
};

Approach) Brute Force

var middleNode = function(head) {
    let node = head;
    let memory = [];
    
    while(node!= null){
        memory.push(node);
        node = node.next;
    }
    
    return memory[Math.floor(memory.length/2)];
};

Conclusion

That’s all folks! In this post, we solved LeetCode problem 876. Middle of the Linked List

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