Initial attempt at add-two-numbers.

.gitignore

@@ -1 +1,2 @@
-*.dSYM
+*.dSYM
+.vscode

add-two-numbers/.gitignore

@@ -0,0 +1 @@
+addTwoNumbers

add-two-numbers/Makefile

@@ -0,0 +1,5 @@
+addTwoNumbers: addTwoNumbers.c
+	gcc -g -Wall -std=gnu99 -o addTwoNumbers addTwoNumbers.c
+
+run: addTwoNumbers
+	./addTwoNumbers

add-two-numbers/addTwoNumbers.c

@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     struct ListNode *next;
+ * };
+ */
+ struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
+    struct ListNode *first = NULL, *current = NULL;
+    while (l1 != NULL) {
+        if (current == NULL) {
+            current = malloc(sizeof(struct ListNode));
+            first = current;
+        } else {
+            current->next = malloc(sizeof(struct ListNode));
+            current = current->next;
+        }
+        current->val = l1->val + l2->val;
+        l1 = l1->next;
+        l2 = l2->next;
+    }
+    return first;
+}
+
+int main() {
+    struct ListNode *l1 = malloc(sizeof(struct ListNode));
+    l1->val = 1;
+    l1->next = malloc(sizeof(struct ListNode));
+    l1->next->val = 2;
+    l1->next->next = NULL;
+
+    struct ListNode *l2 = malloc(sizeof(struct ListNode));
+    l2->val = 3;
+    l2->next = malloc(sizeof(struct ListNode));
+    l2->next->val = 4;
+    l2->next->next = NULL;
+
+    struct ListNode *result = addTwoNumbers(l1, l2);
+    printf("[%d, %d]\n", result->val, result->next->val);
+
+    return 0;
+}