[CPP] 21. Merge Two Sorted Lists

Author: UnresolvedCold

cpp/21-Merge-Two-Sorted-Lists.cpp

@@ -0,0 +1,46 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
+        ListNode* res = new ListNode(0);
+        auto ptr = res;
+        
+        auto ptr1 = list1;
+        auto ptr2 = list2;
+        
+        while (ptr1 && ptr2) {
+            if (ptr1->val < ptr2->val) {
+                res->next = ptr1;
+                ptr1 = ptr1->next;
+                res = res->next;
+            }
+            else {
+                res->next = ptr2;
+                ptr2 = ptr2->next;
+                res = res->next;
+            }
+        }
+        
+        while (ptr1) {
+            res->next = ptr1;
+            res = res->next;
+            ptr1 = ptr1->next;
+        }
+        while (ptr2) {
+            res->next = ptr2;
+            res = res->next;
+            ptr2 = ptr2->next;
+        }
+        
+        return ptr->next;
+    }
+};