Add a TBC solution to leetcode

leetcode/solutions.org

@@ -16,7 +16,7 @@ bool containsDuplicate(vector<int> &nums)
 {
   std::sort(nums.begin(), nums.end());
   const size_t n = nums.size() - 1;
-  for (const size_t i = 0; i < n; ++i)
+  for (const size_t i = 0; i < n - 1; ++i)
     if (nums[i] == nums[i + 1])
       return true;
   return false;
@@ -590,4 +590,85 @@ vector<int> dailyTemperatures(vector<int> &temperatures)
   return days;
 }
 #+end_src
+* Linked Lists
+** TODO (#2) Add two numbers
+Given two linked lists representing the digits of a number in reverse
+order, return their sum.
+#+begin_src c++ :tangle 2.cpp :comments link
+#include <bits/stdc++.h>
+using namespace std;
+
+struct ListNode
+{
+  int val;
+  ListNode *next;
+
+  ListNode() : val{0}, next{nullptr}
+  {
+  }
+
+  ListNode(int val) : val{val}, next{nullptr}
+  {
+  }
+
+  ListNode(int val, ListNode *next) : val{val}, next{next}
+  {
+  }
+
+  ~ListNode()
+  {
+    if (next)
+      delete next;
+  }
+};
+
+ListNode *addTwoNumbers(ListNode *l1, ListNode *l2)
+{
+  if (!(l1 && l2) ||
+      (l1->val == l2->val && l1->val == 0 && !(l1->next || l2->next)))
+    return l1;
+
+  int carry = 0;
+  int sum   = l1->val + l2->val;
+
+  ListNode *root = new ListNode(sum % 10);
+  ListNode *end  = root;
+
+  carry = sum / 10;
+  l1    = l1->next;
+  l2    = l2->next;
+
+  for (; l1 && l2; l1 = l1->next, l2 = l2->next)
+  {
+    sum   = l1->val + l2->val + carry;
+    carry = sum / 10;
+    sum %= 10;
+
+    auto node = new ListNode(sum, nullptr);
+    end->next = node;
+    end       = node;
+  }
+
+  if (l1 || l2)
+  {
+    auto remaining = l1 ? l1 : l2;
+    for (; remaining; remaining = remaining->next)
+    {
+      remaining->val += carry;
+      carry = remaining->val / 10;
+      remaining->val %= 10;
+      end->next = remaining;
+      end       = remaining;
+    }
+  }
+
+  if (carry != 0)
+  {
+    auto node = new ListNode(carry, nullptr);
+    end->next = node;
+  }
+
+  return root;
+}
+#+end_src
 * Blind 75