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876. Middle of the Linked List

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

Solutions

• Java
• C++
• Python
• Go
• TypeScript
• Php
• RenderScript

• /**
   * Definition for singly-linked list.
   * public class ListNode {
   *     int val;
   *     ListNode next;
   *     ListNode() {}
   *     ListNode(int val) { this.val = val; }
   *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
   * }
   */
  class Solution {
      public ListNode middleNode(ListNode head) {
          ListNode slow = head, fast = head;
          while (fast != null && fast.next != null) {
              slow = slow.next;
              fast = fast.next.next;
          }
          return slow;
      }
  }
  

• /**
   * Definition for singly-linked list.
   * struct ListNode {
   *     int val;
   *     ListNode *next;
   *     ListNode() : val(0), next(nullptr) {}
   *     ListNode(int x) : val(x), next(nullptr) {}
   *     ListNode(int x, ListNode *next) : val(x), next(next) {}
   * };
   */
  class Solution {
  public:
      ListNode* middleNode(ListNode* head) {
          ListNode *slow = head, *fast = head;
          while (fast && fast->next) {
              slow = slow->next;
              fast = fast->next->next;
          }
          return slow;
      }
  };
  

• # Definition for singly-linked list.
  # class ListNode:
  #     def __init__(self, val=0, next=None):
  #         self.val = val
  #         self.next = next
  class Solution:
      def middleNode(self, head: ListNode) -> ListNode:
          slow = fast = head
          while fast and fast.next:
              slow, fast = slow.next, fast.next.next
          return slow
  
  

• /**
   * Definition for singly-linked list.
   * type ListNode struct {
   *     Val int
   *     Next *ListNode
   * }
   */
  func middleNode(head *ListNode) *ListNode {
  	slow, fast := head, head
  	for fast != nil && fast.Next != nil {
  		slow, fast = slow.Next, fast.Next.Next
  	}
  	return slow
  }
  

• /**
   * Definition for singly-linked list.
   * class ListNode {
   *     val: number
   *     next: ListNode | null
   *     constructor(val?: number, next?: ListNode | null) {
   *         this.val = (val===undefined ? 0 : val)
   *         this.next = (next===undefined ? null : next)
   *     }
   * }
   */
  
  function middleNode(head: ListNode | null): ListNode | null {
      let fast = head,
          slow = head;
      while (fast != null && fast.next != null) {
          fast = fast.next.next;
          slow = slow.next;
      }
      return slow;
  }
  
  

• /**
   * Definition for a singly-linked list.
   * class ListNode {
   *     public $val = 0;
   *     public $next = null;
   *     function __construct($val = 0, $next = null) {
   *         $this->val = $val;
   *         $this->next = $next;
   *     }
   * }
   */
  class Solution {
      /**
       * @param ListNode $head
       * @return ListNode
       */
      function middleNode($head) {
          $count = 0;
          $tmpHead = $head;
          while ($tmpHead != null) {
              $tmpHead = $tmpHead->next;
              $count++;
          }
          $len = $count - floor($count / 2);
          while ($count != $len) {
              $head = $head->next;
              $count--;
          }
          return $head;
      }
  }
  

• // Definition for singly-linked list.
  // #[derive(PartialEq, Eq, Clone, Debug)]
  // pub struct ListNode {
  //   pub val: i32,
  //   pub next: Option<Box<ListNode>>
  // }
  //
  // impl ListNode {
  //   #[inline]
  //   fn new(val: i32) -> Self {
  //     ListNode {
  //       next: None,
  //       val
  //     }
  //   }
  // }
  impl Solution {
      pub fn middle_node(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
          let mut slow = &head;
          let mut fast = &head;
          while fast.is_some() && fast.as_ref().unwrap().next.is_some() {
              slow = &slow.as_ref().unwrap().next;
              fast = &fast.as_ref().unwrap().next.as_ref().unwrap().next;
          }
          slow.clone()
      }
  }
  
  

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