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Solution.java
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Solution.java
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/**
* Definition for singly-linked list.
* class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
public void reorderList(ListNode head) {
if(head == null)
return;
ListNode slow = head;
ListNode fast = head;
while(fast != null && fast.next != null) {
slow = slow.next;
fast = fast.next.next;
}
ListNode p2 = slow.next;
slow.next = null;
ListNode p1 = head;
p2 = reverse(p2);
ListNode next1;
ListNode next2;
while(p2 != null) {
next1 = p1.next;
next2 = p2.next;
p1.next = p2;
p2.next = next1;
p1 = next1;
p2 = next2;
}
}
private ListNode reverse(ListNode head) {
ListNode node = null;
ListNode next;
while(head != null) {
next = head.next;
head.next = node;
node = head;
head = next;
}
return node;
}
}