refactor 148

fishercoder1534 · fishercoder1534 · commit 132a4e11ae44 · 2018-05-07T07:33:44.000-07:00
diff --git a/src/main/java/com/fishercoder/solutions/_148.java b/src/main/java/com/fishercoder/solutions/_148.java
@@ -9,54 +9,57 @@
  */
 public class _148 {
 
-    /**Credit: https://discuss.leetcode.com/topic/18100/java-merge-sort-solution
-     * But this is not using constant space.*/
-    public ListNode sortList(ListNode head) {
-        if (head == null || head.next == null) {
-            return head;
-        }
+    public static class Solution1 {
+        /**
+         * Credit: https://discuss.leetcode.com/topic/18100/java-merge-sort-solution
+         * But this is not using constant space.
+         */
+        public ListNode sortList(ListNode head) {
+            if (head == null || head.next == null) {
+                return head;
+            }
 
-        //Step 1: split the list into halves
-        ListNode prev = null;
-        ListNode slow = head;
-        ListNode fast = head;
-        while (fast != null && fast.next != null) {
-            prev = slow;
-            fast = fast.next.next;
-            slow = slow.next;
-        }
-        prev.next = null;
+            //Step 1: split the list into halves
+            ListNode prev = null;
+            ListNode slow = head;
+            ListNode fast = head;
+            while (fast != null && fast.next != null) {
+                prev = slow;
+                fast = fast.next.next;
+                slow = slow.next;
+            }
+            prev.next = null;
 
-        //step 2: sort each half
-        ListNode l1 = sortList(head);
-        ListNode l2 = sortList(slow);
+            //step 2: sort each half
+            ListNode l1 = sortList(head);
+            ListNode l2 = sortList(slow);
 
-        //step 3: merge the two halves
-        return merge(l1, l2);
-    }
+            //step 3: merge the two halves
+            return merge(l1, l2);
+        }
 
-    private ListNode merge(ListNode l1, ListNode l2) {
-        ListNode result = new ListNode(0);
-        ListNode tmp = result;
+        private ListNode merge(ListNode l1, ListNode l2) {
+            ListNode result = new ListNode(0);
+            ListNode tmp = result;
 
-        while (l1 != null && l2 != null) {
-            if (l1.val < l2.val) {
+            while (l1 != null && l2 != null) {
+                if (l1.val < l2.val) {
+                    tmp.next = l1;
+                    l1 = l1.next;
+                } else {
+                    tmp.next = l2;
+                    l2 = l2.next;
+                }
+                tmp = tmp.next;
+            }
+
+            if (l1 != null) {
                 tmp.next = l1;
-                l1 = l1.next;
-            } else {
+            }
+            if (l2 != null) {
                 tmp.next = l2;
-                l2 = l2.next;
             }
-            tmp = tmp.next;
-        }
-
-        if (l1 != null) {
-            tmp.next = l1;
-        }
-        if (l2 != null) {
-            tmp.next = l2;
+            return result.next;
         }
-        return result.next;
     }
-
 }
