solves sort list in java

Author: anishLearnsToCode

README.md

@@ -132,7 +132,7 @@
 | 145  | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal)                                                          |                     [![Java](assets/java.png)](src/BinaryTreePostorderTraversal.java) [![Python](assets/python.png)](python/binary_tree_postorder_traversal.py)                      |                                                                                                                                   |
 | 146  | [LRU Cache](https://leetcode.com/problems/lru-cache)                                                                                                      |                                                                    [![Java](assets/java.png)](src/LRUCache.java)                                                                     |                                                                                                                                   |
 | 147  | [Insertion Sort List](https://leetcode.com/problems/insertion-sort-list)                                                                                  |                                                                [![Java](assets/java.png)](src/InsertionSortList.java)                                                                |                                                                                                                                   |
-| 148  | [Sort List](https://leetcode.com/problems/sort-list)                                                                                                      |                                                                                                                                                                                      |                                                                                                                                   |
+| 148  | [Sort List](https://leetcode.com/problems/sort-list)                                                                                                      |                                                                    [![Java](assets/java.png)](src/SortList.java)                                                                     |                                                                                                                                   |
 | 150  | [Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation)                                                        |                                                                                                                                                                                      |                                                                                                                                   |
 | 151  | [Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string)                                                                      |                                                                                                                                                                                      |                                                                                                                                   |
 | 152  | [Maximum Product Subarray](https://leetcode.com/problems/maximum-product-subarray)                                                                        |                                                                                                                                                                                      |                                                                                                                                   |

src/SortList.java

@@ -0,0 +1,41 @@
+// https://leetcode.com/problems/sort-list
+// T: O(N log(N))
+// S: O(log(N))
+
+public class SortList {
+    public ListNode sortList(ListNode head) {
+        if (head == null || head.next == null) return head;
+        ListNode mid = getMid(head);
+        ListNode left = sortList(head);
+        ListNode right = sortList(mid);
+        return merge(left, right);
+    }
+
+    ListNode merge(ListNode list1, ListNode list2) {
+        ListNode dummyHead = new ListNode();
+        ListNode tail = dummyHead;
+        while (list1 != null && list2 != null) {
+            if (list1.val < list2.val) {
+                tail.next = list1;
+                list1 = list1.next;
+            } else {
+                tail.next = list2;
+                list2 = list2.next;
+            }
+            tail = tail.next;
+        }
+        tail.next = (list1 != null ? list1 : list2);
+        return dummyHead.next;
+    }
+
+    ListNode getMid(ListNode head) {
+        ListNode midPrev = null;
+        while (head != null && head.next != null) {
+            midPrev = (midPrev == null ? head : midPrev.next);
+            head = head.next.next;
+        }
+        ListNode mid = midPrev.next;
+        midPrev.next = null;
+        return mid;
+    }
+}