0x08-recursion

0x08. C - Recursion

Recursion is the process of repeating items in a self-similar way. In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.

void recursion() {
   recursion(); /* function calls itself */
}

int main() {
   recursion();
}

Recursion is a technique where we solve a problem by first solving a much smaller one. It the following projects, I put my knowledge of recursion to the test.

NOTE: my algorithms may not be 100% accurate.

0. She locked away a secret, deep inside herself, something she once knew to be true... but chose to forget

Write a function that prints a string, followed by a new line.

• Prototype: void _puts_recursion(char *s);

FYI: The standard library provides a similar function: puts. Run man puts to learn more.

solution

1. Why is it so important to dream? Because, in my dreams we are together

Write a function that prints a string in reverse.

• Prototype: void _print_rev_recursion(char *s);

solution

2. Dreams feel real while we're in them. It's only when we wake up that we realize something was actually strange

Write a function that returns the length of a string.

• Prototype: int _strlen_recursion(char *s);

FYI: The standard library provides a similar function: strlen. Run man strlen to learn more.

solution

3. You mustn't be afraid to dream a little bigger, darling

Write a function that returns the factorial of a given number.

• Prototype: int factorial(int n);

• If n is lower than 0, the function should return -1 to indicate an error

• Factorial of 0 is 1

solution

4. Once an idea has taken hold of the brain it's almost impossible to eradicate

Write a function that returns the value of x raised to the power of y.

• Prototype: int _pow_recursion(int x, int y);

• If y is lower than 0, the function should return -1

FYI: The standard library provides a different function: pow. Run man pow to learn more.

solution

5. Your subconscious is looking for the dreamer

Write a function that returns the natural square root of a number.

• Prototype: int _sqrt_recursion(int n);

• If n does not have a natural square root, the function should return -1

FYI: The standard library provides a different function: sqrt. Run man sqrt to learn more.

solution

6. Inception. Is it possible?

Write a function that returns 1 if the input integer is a prime number, otherwise return 0.

• Prototype: int is_prime_number(int n);

solution

7. They say we only use a fraction of our brain's true potential. Now that's when we're awake. When we're asleep, we can do almost anything

Write a function that returns 1 if a string is a palindrome and 0 if not.

• Prototype: int is_palindrome(char *s);

• An empty string is a palindrome

solution

8. Inception. Now, before you bother telling me it's impossible...

Write a function that compares two strings and returns 1 if the strings can be considered identical, otherwise return 0.

• Prototype: int wildcmp(char *s1, char *s2);
• s2 can contain the special character *.
• The special char * can replace any string (including an empty string)

solution