链表重排序

Author: DmrfCoder

LeetCode/Doc/链表重排序.md

@@ -0,0 +1,34 @@
+# reorder-list（链表重排序）
+
+<center>知识点：链表</center>
+
+
+## 题目描述
+
+Given a singly linked list$ L: L_0→L_1→…→L{n-1}→L_n​$,
+reorder it to: $L_0→L_n →L_1→L_{n-1}→L_2→L_{n-2}→…​$
+
+You must do this in-place without altering the nodes' values.
+
+For example,
+Given{1,2,3,4}, reorder it to{1,4,2,3}.
+
+给定一个链表$ L: L_0→L_1→…→L{n-1}→L_n$,
+将其重排序为： $L_0→L_n →L_1→L_{n-1}→L_2→L_{n-2}→…​$
+你必须在不改变节点值的情况下完成。
+比如：
+给定{1,2,3,4},重排序为：{1,4,2,3}
+
+## 解题思路
+
+比如：$ L: L_0→L_1→…→L{n-1}→L_n​$，首先利用快慢指针将该链表分为两个部分：
+
+$L_a:L_0→L_1→…L_{\frac{n}{2}}$,
+
+$L_b:L_{\frac{n}{2}+1}→L_{\frac{n}{2}+2}→…L_{n}$
+
+然后将$L_b$翻转，然后合并$L_a$和$L_b$即可。
+
+## 代码
+
+[这里](../src/eight/Solution.java)

LeetCode/out/production/LeetCode/eight/ListNode.class

@@ -0,0 +1,76 @@
+package eight;
+
+/**
+ * @author dmrfcoder
+ * @date 2019/4/10
+ */
+
+/**
+ * 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 && head.next != null) {
+            ListNode fast, slow;
+            fast = slow = head;
+            //快慢指针找出链表的中间节点
+            while (fast.next != null && fast.next.next != null) {
+                fast = fast.next.next;
+                slow = slow.next;
+            }
+
+            //拆分链表
+            ListNode preNode = slow.next;
+            slow.next = null;
+            ListNode afterNode = preNode.next;
+            preNode.next=null;
+            //翻转后一半链表
+            while (afterNode != null) {
+                ListNode tempNode = afterNode.next;
+                afterNode.next = preNode;
+                preNode = afterNode;
+                afterNode = tempNode;
+            }
+
+            //合并链表
+            while (preNode != null && head != null) {
+                ListNode tempNode1 = head.next;
+                ListNode tempNode2 = preNode.next;
+                head.next = preNode;
+                preNode.next = tempNode1;
+                preNode = tempNode2;
+                head = tempNode1;
+
+            }
+
+
+        }
+
+    }
+
+
+    public static void main(String[] args) {
+        ListNode head = new ListNode(1);
+        ListNode node2 = new ListNode(2);
+        ListNode node3 = new ListNode(3);
+        ListNode node4 = new ListNode(4);
+        ListNode node5 = new ListNode(5);
+
+        head.next = node2;
+        node2.next = node3;
+        node3.next = node4;
+        node4.next = node5;
+        Solution solution = new Solution();
+        solution.reorderList(head);
+    }
+}

LeetCode/out/production/LeetCode/eight/Solution.class

@@ -149,4 +149,5 @@
 - [insertion-sort-list(使用插入排序对链表进行排序)](./LeetCode/Doc/使用插入排序对链表进行排序.md)
 - [binary-tree-postorder-traversal（后序遍历二叉树）](./LeetCode/Doc/后序遍历二叉树.md)
 - [binary-tree-preorder-traversal（先序遍历二叉树）](./LeetCode/Doc/先序遍历二叉树.md)
+- [reorder-list（链表重排序）](./LeetCode/Doc/链表重排序.md)