In Rust it\'s not possible to have:\n* an imutable reference and a mutable reference pointing to the same object\n* more than one mutable references to the same object\n\nTherefore, it\'s not possible to properly implement the "slow/fast pointer" solution for "876-Middle of the Linked List".\nThe current list definition is:\n\n```rust\nhead: Option<Box<ListNode>>\n```\n\n```rust\npub struct ListNode {\n    pub val: i32,\n    pub next: Option<Box<ListNode>>,\n}\n```\n\nSo it\'s not possible to have a mutable "slow" pointer and an immutable "fast" pointer, nor mutable "slow" and "fast" pointers. The current workaround is to clone the list, which leaves a bad taste in the mouth:\n\n```rust\nimpl Solution {\n    pub fn middle_node(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {\n        let mut fast = head.as_ref();\n        let mut slow = head.as_ref();\n\n        while let Some(node) = fast {\n            match node.next.as_ref() {\n                None => break,\n                Some(fast_next) => {\n                    fast = fast_next.next.as_ref();\n                    slow = slow.unwrap().next.as_ref();\n                }\n            }\n        }\n\n        // this clones all the nodes after (and including) "slow"\n        slow.map(|n| n.clone())\n    }\n}\n```\n\nIt would have been much better if the method signature was:\n```rust\n    pub fn middle_node(head: &Option<Box<ListNode>>) -> &Option<Box<ListNode>> {\n```\n\nor even\n```rust\n    pub fn middle_node(head: Option<Rc<ListNode>>) -> Option<Rc<ListNode>> {\n```\n\nwhich would have avoided the issue\n\nPS: The same applies to "19. Remove Nth Node From End of List"

In Rust it\'s not possible to have:\n an imutable reference and a mutable reference pointing to the same object\n more than one mutable references to the same o