876. 链表的中间结点🔖链表

/**
 * 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 count = 0
    let temp = head
    while(temp) {
        count++
        temp = temp.next
    }
    for(let i = 0; i < (count-1)/2; i++) {
        head = head.next
    }
    return head
};

class Solution {
    public ListNode middleNode(ListNode head) {
        if (head.next == null) return head;
        if (head.next.next == null) return head.next;

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