fix: resolve memory leak issue in No.0002 (#4434)

Author: gaganxsaini

solution/0000-0099/0002.Add Two Numbers/README.md

@@ -147,9 +147,9 @@ class Solution {
 class Solution {
 public:
     ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
-        ListNode* dummy = new ListNode();
+        ListNode dummy;
         int carry = 0;
-        ListNode* cur = dummy;
+        ListNode* cur = &dummy;
         while (l1 || l2 || carry) {
             int s = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + carry;
             carry = s / 10;
@@ -158,7 +158,7 @@ public:
             l1 = l1 ? l1->next : nullptr;
             l2 = l2 ? l2->next : nullptr;
         }
-        return dummy->next;
+        return dummy.next;
     }
 };
 ```

solution/0000-0099/0002.Add Two Numbers/README_EN.md

@@ -143,9 +143,9 @@ class Solution {
 class Solution {
 public:
     ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
-        ListNode* dummy = new ListNode();
+        ListNode dummy;
         int carry = 0;
-        ListNode* cur = dummy;
+        ListNode* cur = &dummy;
         while (l1 || l2 || carry) {
             int s = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + carry;
             carry = s / 10;
@@ -154,7 +154,7 @@ public:
             l1 = l1 ? l1->next : nullptr;
             l2 = l2 ? l2->next : nullptr;
         }
-        return dummy->next;
+        return dummy.next;
     }
 };
 ```

solution/0000-0099/0002.Add Two Numbers/Solution.cpp

@@ -11,9 +11,9 @@
 class Solution {
 public:
     ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
-        ListNode* dummy = new ListNode();
+        ListNode dummy;
         int carry = 0;
-        ListNode* cur = dummy;
+        ListNode* cur = &dummy;
         while (l1 || l2 || carry) {
             int s = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + carry;
             carry = s / 10;
@@ -22,6 +22,6 @@ class Solution {
             l1 = l1 ? l1->next : nullptr;
             l2 = l2 ? l2->next : nullptr;
         }
-        return dummy->next;
+        return dummy.next;
     }
 };