All kinds of fibonacci solutions

fib_tree.c

#include <stdio.h>
#include <stdlib.h>

struct fib_node {
  int n;
  struct fib_node *left, *right;
};

struct fib_node* fib(int n) {
  struct fib_node *node;

  node = malloc(sizeof(struct fib_node));
  node->n = n;
  
  if (n && (n - 1)) {
    node->left  = fib(n-1);
    node->right = fib(n-2);
  }

  return node;               
}

int count_leaves(struct fib_node *node) {
    if (node->left && node->right) {
        return count_leaves(node->left) + 
               count_leaves(node->right);
    }
    return node->n;
}

void main(void) {
  // displays 13, the 7th fib number
  printf("%d\n", count_leaves(fib(7)));
}

genfib.py

# fib using recursive generator

def fibgen(n, a=0, b=1):
    yield a
    if n > 0:
        yield from fibgen(n-1, b, a+b)

    
def fib(n):
    return list(fibgen(n))[n]

print(fib(7))