Leetcode 21 Merge Two Sorted Lists

jiajionline · Jul 1, 2023 · 0ec8623 · 0ec8623
1 parent f46985d
commit 0ec8623
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Showing 2 changed files with 29 additions and 29 deletions.
diff --git a/0021_Merge Two Sorted Lists/MergeTwoSortedLists.java b/0021_Merge Two Sorted Lists/MergeTwoSortedLists.java
@@ -2,12 +2,29 @@ class Solution {
     public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
         if(list1 == null) return list2;
         if(list2 == null) return list1;
-        if(list1.val <= list2.val) {
-            list1.next = mergeTwoLists(list1.next, list2);
-            return list1;
-        }else{
-            list2.next = mergeTwoLists(list1, list2.next);
-            return list2;
+
+        ListNode preHead = new ListNode();
+        ListNode curr = preHead;
+
+        ListNode p1 = list1;
+        ListNode p2 = list2;
+
+        while(p1!=null && p2!=null)
+        {
+            if(p1.val <= p2.val){
+                curr.next = p1;
+                p1 = p1.next;
+            }else{
+                curr.next = p2;
+                p2 = p2.next;
+            }
+
+            curr = curr.next;
         }
+
+        if(p1!=null) curr.next = p1;
+        if(p2!=null) curr.next = p2;
+
+        return preHead.next;
     }
 }
diff --git a/0021_Merge Two Sorted Lists/MergeTwoSortedLists_Recursion.java b/0021_Merge Two Sorted Lists/MergeTwoSortedLists_Recursion.java
@@ -2,29 +2,12 @@ class Solution {
     public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
         if(list1 == null) return list2;
         if(list2 == null) return list1;
-
-        ListNode preHead = new ListNode();
-        ListNode curr = preHead;
-
-        ListNode p1 = list1;
-        ListNode p2 = list2;
-
-        while(p1!=null && p2!=null)
-        {
-            if(p1.val <= p2.val){
-                curr.next = p1;
-                p1 = p1.next;
-            }else{
-                curr.next = p2;
-                p2 = p2.next;
-            }
-
-            curr = curr.next;
+        if(list1.val <= list2.val) {
+            list1.next = mergeTwoLists(list1.next, list2);
+            return list1;
+        }else{
+            list2.next = mergeTwoLists(list1, list2.next);
+            return list2;
         }
-
-        if(p1!=null) curr.next = p1;
-        if(p2!=null) curr.next = p2;
-
-        return preHead.next;
     }
 }