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876. Middle of the Linked List
Given a non-empty, singly linked list with head node head, return a middle node of linked list.
If there are two middle nodes, return the second middle node.
Example 1:
Input: [1,2,3,4,5]
Output: Node 3 from this list (Serialization: [3,4,5])
The returned node has value 3. (The judge's serialization of this node is [3,4,5]).
Note that we returned a ListNode object ans, such that:
ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.Example 2:
Input: [1,2,3,4,5,6]
Output: Node 4 from this list (Serialization: [4,5,6])
Since the list has two middle nodes with values 3 and 4, we return the second one.Note:
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The number of nodes in the given list will be between
1and100.
解题分析
快慢指针，注意最后节点的处理。
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一刷
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二刷
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/**
* 快慢指针
*
* @author D瓜哥 · https://www.diguage.com
* @since 2024-07-02 20:22:30
*/
public ListNode middleNode(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode slow = head;
ListNode fast = head;
while (fast.next != null && fast.next.next != null) {
slow = slow.next;
fast = fast.next.next;
}
return fast.next == null ? slow : slow.next;
}
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/**
* 快慢指针
*
* @author D瓜哥 · https://www.diguage.com
* @since 2024-09-15 23:20:35
*/
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;
}