Create 04.cc

solved/LeetCode/Challenges/2020/January/04.cc

@@ -0,0 +1,50 @@
+class Solution {
+public:
+    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
+        ListNode* tail = (val(l1) < val(l2)) ? l1 : l2;
+        ListNode* head = tail;
+        if (tail == l1) {
+            l1 = advance(l1);
+        } else {
+            l2 = advance(l2);
+        }
+
+        while ((l1 != nullptr) && (l2 != nullptr)) {
+            ListNode* next = (val(l1) < val(l2)) ? l1 : l2;
+            if (next == l1) {
+                l1 = advance(l1);
+            } else {
+                l2 = advance(l2);
+            }
+            tail->next = next;
+            tail = advance(tail);
+        }
+
+        while (l1 != nullptr) {
+            tail->next = l1;
+            tail = advance(tail);
+            l1 = advance(l1);
+        }
+
+        while (l2 != nullptr) {
+            tail->next = l2;
+            tail = advance(tail);
+            l2 = advance(l2);
+        }
+        return head;
+    }
+private:
+    ListNode* advance(ListNode* l) {
+        if (l == nullptr) {
+            return l;
+        }
+        return l->next;
+    }
+
+    int val(ListNode* l) {
+        if (l == nullptr) {
+            return 1000;
+        }
+        return l->val;
+    }
+};