First Prime

Difficulty: ⚫◯◯◯ (Easy)

Tags: linked-list, prime-numbers

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

Description

Write a function first_prime that takes one argument head, where head is a pointer to the first node of a linked list.

The function should return the first prime number in the list. If there are no prime numbers in the list, the function should return -1.

A prime number is a whole number greater than 1 that is only exactly divisible (leaving no remainder) by 1 and itself.

Examples

Example 1

Input:  4 -> 11 -> 7 -> 9 -> X
Output: 11

Explanation: 11 is the first prime number in the list.

Example 2

Input:  4 -> 4 -> 4 -> X
Output: -1

Explanation: There are no prime numbers in the list.

Example 3

Input:  2 -> 3 -> 5 -> X
Output: 2

Explanation: 2 is the first (and smallest) prime number.

Function Signature

int first_prime(struct node *head);

Data Structure

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

Constraints

• The value 1 is not considered to be a prime number.
• Return -1 if the list is empty.
• Do not modify the linked list.
• 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).

Test Cases

./first-prime 10 4 15 17
17

./first-prime 5 64 15 99 25
5

./first-prime 1 9
-1

./first-prime 16
-1

./first-prime 2 3 5
2