Merge pull request neetcode-gh#2479 from Anukriti167/patch-4

Update 0148-sort-list.java

Author: a93a

java/0148-sort-list.java

@@ -1,3 +1,64 @@
+/**
+ * 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 {
+    // Merge Sort Implementation
+    public ListNode getMid(ListNode head){
+        ListNode slow=head, fast=head.next;
+        while(fast != null && fast.next != null){
+            fast = fast.next.next;
+            slow = slow.next;
+        }
+        return slow;
+    }
+    public ListNode merge(ListNode left, ListNode right){
+        ListNode dummy = new ListNode();
+        ListNode tail = dummy;
+
+        while(left != null && right != null){
+            if(left.val < right.val){
+                tail.next = left;
+                left = left.next;
+            }else{
+                tail.next = right;
+                right = right.next;
+            }
+            tail = tail.next;
+        }
+        if(left != null){
+            tail.next = left;
+        }
+        if(right != null){
+            tail.next = right;
+        }
+        return dummy.next;
+    }
+    public ListNode sortList(ListNode head) {
+        if(head == null || head.next == null){
+            return head;
+        }
+
+        // Split the list in 2 halfs
+        ListNode left = head;
+        ListNode right = getMid(head);
+        ListNode tmp = right.next;
+        right.next = null;
+        right = tmp;
+
+        left = sortList(left);
+        right = sortList(right);
+        return merge(left, right);
+    }
+}
+
+// Using a Heap to sort the list
 class Solution {
     public ListNode sortList(ListNode head) {
         if(head == null || head.next == null){