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Problem
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:
The number of nodes in the given list will be between 1 and 100.
Solution
SOL.1
class Solution {
public ListNode middleNode(ListNode head) {
ListNode fast = head, slow = head;
while (fast != null && fast.next != null) {
fast = fast.next.next;
slow = slow.next;
}
return slow;
}
}
SOL.2
class Solution {
public ListNode middleNode(ListNode head) {
ListNode fast = head, slow = head;
int n = 1;
while (fast.next != null) {
fast = fast.next;
n++;
}
int k = n/2;
while (k != 0) {
slow = slow.next;
k–;
}
return slow;
}
}
