Reorder List
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.
class Solution {
public ListNode reverse(ListNode node) {
ListNode prev = null, temp = node;
while (temp != null) {
ListNode t = temp.next;
temp.next = prev;
prev = temp;
temp = t;
}
return prev;
}
public void reorderList(ListNode head) {
if (head == null || head.next == null)
return;
ListNode fast = head, slow = head;
while (fast != null && fast.next != null && fast.next.next != null) {
fast = fast.next.next;
slow = slow.next;
}
ListNode rightSide = reverse(slow.next);
slow.next = null;
ListNode leftSide = head;
while (leftSide != null && rightSide!=null) {
ListNode temp1 = leftSide.next;
ListNode temp2 = rightSide.next;
leftSide.next = rightSide;
rightSide.next = temp1;
leftSide = temp1;
rightSide = temp2;
}
}
}
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