fixed problem 2

Signed-off-by: Krishna Vedala <7001608+kvedala@users.noreply.github.com>

leetcode/problem_2/sol1.c

@@ -1,11 +1,33 @@
-/*
- * Definition for singly-linked list.
- * struct ListNode {
- *     int val;
- *     struct ListNode *next;
- * };
+/**
+ * \file
+ * \brief [2. Add two numbers](https://leetcode.com/problems/add-two-numbers/)
+ * solution \details You are given two non-empty linked lists representing two
+ * non-negative integers. The digits are stored in reverse order, and each of
+ * their nodes contains a single digit. Add the two numbers and return the sum
+ * as a linked list.
  */
 
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/**
+ * @brief Definition for singly-linked list.
+ */
+struct ListNode
+{
+    int val;               /**< value at node */
+    struct ListNode *next; /**< pointer to next node in the list */
+};
+
+/**
+ * @brief Solution implementation
+ *
+ * @param l1 first number with digits represented as linked list
+ * @param l2 second number with digits represented as linked list
+ * @return resulting number with digits represented as linked list
+ */
 struct ListNode *addTwoNumbers(struct ListNode *l1, struct ListNode *l2)
 {
     struct ListNode *head = NULL;
@@ -55,3 +77,99 @@ struct ListNode *addTwoNumbers(struct ListNode *l1, struct ListNode *l2)
 
     return head;
 }
+
+/**
+ * @brief Function to free dynamically allocated list
+ *
+ * @param node pointer to head of the list
+ */
+void free_list(struct ListNode *node)
+{
+    if (node->next != NULL)
+        free_list(node->next);
+
+    free(node);
+    node = NULL;
+};
+
+/**
+ * @brief Generate a node list from an array of digits
+ *
+ * @param num array of digits. index of units place is '0'
+ * @param num_digits total number of digits
+ * @return pointer to the node containing the units place of the number
+ */
+struct ListNode *list_from_array(const unsigned char num[],
+                                 unsigned int num_digits)
+{
+    struct ListNode *prev_node = NULL;
+    struct ListNode *root_node = NULL;
+
+    for (unsigned int i = 0; i < num_digits; i++)
+    {
+        struct ListNode *node = malloc(sizeof(struct ListNode));
+        node->val = num[i];
+        node->next = NULL;
+        if (!prev_node)
+        {
+            prev_node = node;
+            root_node = node;
+        }
+        else
+        {
+            prev_node->next = node;
+            prev_node = node;
+        }
+    }
+
+    return root_node;
+}
+
+/**
+ * @brief Support function to print the list of digits
+ *
+ * @param node pointer to units digit
+ * @return string representation of the digits with units place to he left
+ */
+const char *print_list(const struct ListNode *node)
+{
+    static char out_str[256];
+    memset(out_str, '\0', 256);
+    const struct ListNode *ptr = node;
+    while (ptr)
+    {
+        if (ptr == node)
+            snprintf(out_str, 256, "%d", ptr->val);
+        else
+            snprintf(out_str, 256, "%s, %d", out_str, ptr->val);
+        ptr = ptr->next;
+    }
+
+    return out_str;
+}
+
+/**
+ * @brief Main function
+ * @return 0
+ */
+int main()
+{
+    unsigned char num1[] = {2, 4, 3};
+    struct ListNode *l1 = list_from_array(num1, 3);
+    unsigned char num2[] = {5, 6, 4};
+    struct ListNode *l2 = list_from_array(num2, 3);
+    struct ListNode *out1 = addTwoNumbers(l1, l2);
+
+    printf("<%s> + ", print_list(l1));
+    printf("<%s> = ", print_list(l2));
+    printf("<%s>\n", print_list(out1));
+    assert(out1->val == 7 && out1->next->val == 0 &&
+           out1->next->next->val == 8);
+    printf("Test 1 passed.\n");
+
+    free_list(l1);
+    free_list(l2);
+    free_list(out1);
+
+    return 0;
+}