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leetcode143.java
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leetcode143.java
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/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode reverseList(ListNode head) {
ListNode newHead = null;
while(head != null){
ListNode next = head.next;
head.next = newHead;
newHead = head;
head = next;
}
return newHead;
}
public void reorderList(ListNode head) {
if(head==null||head.next==null)
return;
ListNode mid = head;
ListNode end = head;
// find the middle node, p1 denotes the middle node
while(end.next != null && end.next.next != null){
mid = mid.next;
end = end.next.next;
}
end = mid.next;
// divide into two lists
mid.next = null;
// reverse list after middle node
mid = reverseList(end);
// reorder list
ListNode cur = head;
while(mid != null){
ListNode tmp = cur.next;
cur.next = mid;
mid = mid.next;
cur = cur.next;
cur.next = tmp;
cur = cur.next;
}
}
}