public/subjects/how_many_references/README.md

## how many references

### Instructions

Create the following functions :

- `add_ele` that adds an element to the value in the `Node`
- `how_many_references` that returns how many times the value is referenced in the code
- `rm_all_ref` that receives a `Rc<String>` and removes all elements from the vector that
  are equal to that value, this should only happen if the two Rcs point to the same allocation

### Expected Function

```rust
pub use std::rc::Rc;

pub struct Node {
    pub value: Vec<Rc<String>>,
}

impl Node {
    pub fn new(value: Vec<Rc<String>>) -> Node {
        Node { value: value }
    }
    pub fn add_ele(&mut self, v: Rc<String>) {}
    pub fn rm_all_ref(&mut self, v: Rc<String>) {}
}

pub fn how_many_references(value: &Rc<String>) -> usize {}
```

### Usage

Here is a program to test your function

```rust
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_ele(b.clone());
    new_node.add_ele(a.clone());
    new_node.add_ele(c.clone());
    new_node.add_ele(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
student@ubuntu:~/[[ROOT]]/test$ cargo run
a: 4
b: 2
c: 2
a: 1
b: 2
c: 2
student@ubuntu:~/[[ROOT]]/test$
```

### Notions

- https://doc.rust-lang.org/book/ch15-04-rc.html
- https://doc.rust-lang.org/std/rc/struct.Rc.html