增加排序链表

Author: starsingchow

java/148.排序链表.java

@@ -0,0 +1,78 @@
+/*
+ * @lc app=leetcode.cn id=148 lang=java
+ *
+ * [148] 排序链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode sortList(ListNode head) {
+        return mergeSort(head);
+    }
+
+    public ListNode findMiddle(ListNode node) {
+        ListNode slow = node;
+        ListNode fast = node.next;
+
+        while(fast != null && fast.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+        } 
+
+        return slow;
+    }
+
+    public ListNode mergeTwoLists(ListNode node1, ListNode node2) {
+        ListNode dummy = new ListNode();
+        ListNode head = dummy;
+
+        while(node1 != null && node2 != null) {
+            if(node1.val < node2.val) {
+                head.next = node1;
+                node1 = node1.next;
+            } else {
+                head.next = node2;
+                node2 = node2.next;
+            }
+
+            head = head.next;
+        }
+
+        if(node1 != null) {
+            head.next = node1;
+        }
+
+        if(node2 != null) {
+            head.next = node2;
+        }
+
+        return dummy.next;
+    }
+
+    public ListNode mergeSort(ListNode node) {
+        if(node == null || node.next == null) {
+            return node;
+        }
+
+        ListNode middleNode = findMiddle(node);
+        ListNode middleNodeNext = middleNode.next;
+        middleNode.next = null;
+        
+        ListNode node1 = mergeSort(node);
+        ListNode node2 = mergeSort(middleNodeNext);
+        
+        return mergeTwoLists(node1, node2);
+    }
+}
+// @lc code=end
+