merge-two-sorted-lists solution

Author: hyeri0903

merge-two-sorted-lists/hyeri0903.java

@@ -0,0 +1,40 @@
+/**
+ * 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 mergeTwoLists(ListNode list1, ListNode list2) {
+        /**
+        time: O(n + m)
+        space: O(1)
+         */
+        if(list1 == null) return list2;
+        if(list2 == null) return list1;
+
+        ListNode res = new ListNode();
+        ListNode tmp = res;
+
+        while(list1 != null && list2 != null) {
+            if(list1.val > list2.val) {
+                tmp.next = list2;
+                list2 = list2.next;
+            } else {
+                tmp.next = list1;
+                list1 = list1.next;
+            }
+            tmp = tmp.next;
+        }
+        if(list1 == null) {
+            tmp.next = list2;
+        } else {
+            tmp.next = list1;
+        }
+        return res.next;
+    }
+}