Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…
You may not modify the values in the list’s nodes, only nodes itself may be changed.
Example 1:
Given 1->2->3->4, reorder it to 1->4->2->3.
Example 2:
Given 1->2->3->4->5, reorder it to 1->5->2->4->3.
3step:Find the middle of the list
Reverse the half after middle 1->2->3->4->5->6 to 1->2->3->6->5->4
Start reorder one by one 1->2->3->6->5->4 to 1->6->2->5->3->4
public void reorderList(ListNode head) {
if(head == null || head.next == null) return ;
ListNode slow = head, fast = head;
while(fast.next != null && fast.next.next != null){
slow = slow.next;
fast = fast.next.next;
}
ListNode mid = slow;
ListNode preCur = slow.next;
while(preCur.next != null){
ListNode cur = preCur.next;
preCur.next = cur.next;
cur.next = mid.next;
mid.next = cur;
}
ListNode p = mid.next;
while(head != mid){
mid.next = p.next;
p.next = head.next;
head.next = p;
head = p.next;
p = mid.next;
}
return ;
}