## how many references
### Instructions
Create the following **functions** :
- `add_element` : which adds an element to the list in the `Node` .
- `how_many_references` : which returns how many times the value is referenced in the code.
- `rm_all_ref` : which accepts an `Rc<String>` and removes all elements from the vector that are equal to that value. This should only happen if the two `Rc` s point to the same allocation.
### Expected Functions and structures
```rust
pub use std::rc::Rc;
pub struct Node {
pub ref_list: Vec< Rc < String > >,
}
impl Node {
pub fn new(ref_list: Vec< Rc < String > >) -> Node {
Node { ref_list: ref_list }
}
pub fn add_element(& mut self, element: Rc< String > ) {}
pub fn rm_all_ref(& mut self, element: Rc< String > ) {}
}
pub fn how_many_references(ref_list: & Rc< String > ) -> usize {}
```
### Usage
Here is a program to test your functions,
```rust
use how_many_references::*;
fn main() {
let a = Rc::new(String::from("a"));
let b = Rc::new(String::from("b"));
let c = Rc::new(String::from("c"));
let a1 = Rc::new(String::from("a"));
let mut new_node = Node::new(vec![a.clone()]);
new_node.add_element(b.clone());
new_node.add_element(a.clone());
new_node.add_element(c.clone());
new_node.add_element(a.clone());
println!("a: {:?}", how_many_references(&a));
println!("b: {:?}", how_many_references(&b));
println!("c: {:?}", how_many_references(&c));
new_node.rm_all_ref(a1.clone());
new_node.rm_all_ref(a.clone());
println!("a: {:?}", how_many_references(&a));
println!("b: {:?}", how_many_references(&b));
println!("c: {:?}", how_many_references(&c));
}
```
And its output:
```console
$ cargo run
a: 4
b: 2
c: 2
a: 1
b: 2
c: 2
$
```
### Notions
- [Reference Counted Smart Pointer ](https://doc.rust-lang.org/book/ch15-04-rc.html )
- [Struct std::rc::Rc ](https://doc.rust-lang.org/std/rc/struct.Rc.html )
