Find Middle of Linked List Leetcode

solution.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
  ListNode* middleNode(ListNode* head) {
    if(head==NULL|| head->next==NULL)
      return head;
    
    ListNode* slow = head;
    ListNode* fast = head;
    
    while(fast != NULL && fast->next != NULL){
      fast = fast->next->next;
      slow = slow->next;
    }

    return slow;
  }
};