Compare Tens

Difficulty: ⚫◯◯◯

Tags: linked-list, counting, comparison

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

Description

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

The function should compare the count of two-digit positive numbers (10-99) in each list and return:

• -1 if list1 has fewer two-digit numbers than list2
• 0 if both lists have the same number of two-digit numbers
• 1 if list1 has more two-digit numbers than list2

Two-digit positive numbers: Numbers from 10 to 99 (inclusive).

Examples

Example 1

List 1: 13 -> 1 -> 4 -> X
List 2: 2 -> 71 -> 1 -> 18 -> 3 -> X

List 1 has 1 two-digit number (13)
List 2 has 2 two-digit numbers (71, 18)

Output: -1 (list1 has fewer)

Example 2

List 1: 30 -> 11 -> X
List 2: 19 -> 71 -> X

List 1 has 2 two-digit numbers (30, 11)
List 2 has 2 two-digit numbers (19, 71)

Output: 0 (same count)

Example 3

List 1: 10 -> 16 -> 21 -> 12 -> X
List 2: 16 -> 7 -> 8 -> 12 -> X

List 1 has 4 two-digit numbers (10, 16, 21, 12)
List 2 has 2 two-digit numbers (16, 12)

Output: 1 (list1 has more)

Example 4

List 1: 3 -> 1 -> 4 -> X
List 2: 2 -> 7 -> 1 -> 8 -> 3 -> X

List 1 has 0 two-digit numbers
List 2 has 0 two-digit numbers

Output: 0 (same count)

Example 5

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

List 1 has 0 two-digit numbers
List 2 has 1 two-digit number (42)

Output: -1 (list1 has fewer)

Example 6: Both Empty

List 1: (empty)
List 2: (empty)

Output: 0 (both have 0 two-digit numbers)

Function Signature

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

Data Structure

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

Constraints

• You may assume inputs will be positive integers.
• Two-digit numbers are those from 10 to 99 (inclusive).
• Return only one of three values: -1, 0, or 1.
• 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.

Hints

• Create a helper function to count two-digit numbers in a single list.
• A number is two-digit if: data >= 10 && data <= 99
• Compare the counts and return the appropriate value.

Testing

The command line uses - to separate the two lists.

./compare-tens 3 1 4 - 2 7 1 8 3
0

./compare-tens 10 16 21 12 - 16 7 8 12
1

./compare-tens 2 4 6 - 42
-1

./compare-tens -
0

./compare-tens 13 1 4 - 2 71 1 18 3
-1

./compare-tens 30 11 - 19 71
0