【力扣刷题练习】143. 重排链表

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题目描述：

L0 → L1 → … → Ln - 1 → Ln
请将其重新排列后变为：

L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …
不能只是单纯的改变节点内部的值，而是需要实际的进行节点交换。

题目解答：

class Solution {public ListNode findmidNode(ListNode head) {// 找到中间结点ListNode slow = head, fast = head;while (fast != null && fast.next != null) {slow = slow.next;fast = fast.next.next;}return slow;}public ListNode reverseList(ListNode head) {// 翻转链表ListNode p = head, q = null;while (p != null) {ListNode t = p.next;p.next = q;q = p;p = t;}return q;}public void mergeList(ListNode l1, ListNode l2) {// 合并链表while (l1 != null && l2 != null) {ListNode l1_next = l1.next, l2_next = l2.next;l1.next = l2;l1 = l1_next;l2.next = l1;l2 = l2_next;}}public void reorderList(ListNode head) {if (head == null)return;ListNode mid = findmidNode(head);ListNode l1 = head, l2 = mid.next;mid.next = null;l2 = reverseList(l2);mergeList(l1, l2);}
}