List Product

Difficulty: ⚫◯◯◯

Tags: linked-list, traversal, math

Hurdle: Passing this question is sufficient to pass the linked lists hurdle.

Description

Write a function product that is given two arguments, head1 and head2, which are pointers to the first nodes of two linked lists.

The function should return the sum of the products of corresponding elements from both lists:

• Multiply the 1st element of list1 with the 1st element of list2
• Multiply the 2nd element of list1 with the 2nd element of list2
• And so on...
• Sum all these products together

Important: If one list is longer than the other, the extra elements should be ignored.

Examples

Example 1

List 1: 3 -> 1 -> 4 -> 1 -> 5 -> 9 -> X
List 2: 2 -> 7 -> 9 -> X

Output: 49

Explanation: 3×2 + 1×7 + 4×9 = 6 + 7 + 36 = 49. The extra elements (1, 5, 9) in list1 are ignored.

Example 2

List 1: 2 -> 7 -> X
List 2: 4 -> 42 -> 4242 -> 4242 -> X

Output: 302

Explanation: 2×4 + 7×42 = 8 + 294 = 302. The extra elements in list2 are ignored.

Example 3

List 1: 2 -> 4 -> 6 -> X
List 2: 42 -> X

Output: 84

Explanation: Only 2×42 = 84 (only one pair of corresponding elements).

Example 4

List 1: (empty)
List 2: 1 -> 2 -> 3 -> 4 -> X

Output: 0

Explanation: No corresponding elements, so the result is 0.

Example 5

List 1: 4 -> 3 -> 2 -> 1 -> X
List 2: (empty)

Output: 0

Explanation: No corresponding elements, so the result is 0.

Function Signature

int product(struct node *head1, struct node *head2);

Data Structure

struct node {
    struct node *next;
    int          data;
};

Constraints

• The lists may be different lengths.
• The data fields may contain any integer (positive, negative, or zero).
• product should return only a single integer.
• Do not change the linked lists provided.
• Do not change the next or data fields of list nodes.
• Do not use arrays.
• Do not call malloc.
• Do not call scanf, getchar, or fgets.
• Do not call printf (the function should only return a value).

Hints

• Traverse both lists simultaneously.
• Stop when either list reaches NULL.
• Initialize your sum to 0.

Testing

The command line uses - to separate the two lists.

./list-product 3 1 4 1 5 9 - 2 7 9 8
57

./list-product 16 7 8 12 - 13 19 21 12
653

./list-product 2 4 6 - 42
84

./list-product - 1 2 3 4
0

./list-product 4 3 2 1 -
0

./list-product -
0