rustScope errorHard

Rc cycle prevents memory deallocation

Time: 0:00

BugFind the bug and fix the code

What it should do

Link parent and child nodes cleanly without memory cycle. Example: break_rc_cycle(99) -> 99

What happens instead

Memory leak detected: Rc reference count never drops to zero due to circular ownership

use std::cell::RefCell;
use std::rc::Rc;

struct Node {
    val: i32,
    parent: RefCell<Option<Rc<Node>>>,
}

fn break_rc_cycle(val: i32) -> i32 {
    let parent = Rc::new(Node { val: 1, parent: RefCell::new(None) });
    let child = Rc::new(Node { val, parent: RefCell::new(Some(Rc::clone(&parent))) });
    // Cycle: parent references child, child references parent
    *parent.parent.borrow_mut() = Some(Rc::clone(&child));
    child.val
}

fn main() {
    println!("{}", break_rc_cycle(99));
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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Hints

🏆 0 hints = Flawless Solve

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Hint 3

Unlocks after Hint 2

This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

Learn the scope and closure bugs pattern Step through your own code

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use std::cell::RefCell; use std::rc::Rc; struct Node { val: i32, parent: RefCell<Option<Rc<Node>>>, } fn break_rc_cycle(val: i32) -> i32 { let parent = Rc::new(Node { val: 1, parent: RefCell::new(None) }); let child = Rc::new(Node { val, parent: RefCell::new(Some(Rc::clone(&parent))) }); // Cycle: parent references child, child references parent *parent.parent.borrow_mut() = Some(Rc::clone(&child)); child.val } fn main() { println!("{}", break_rc_cycle(99)); }

Rc cycle prevents memory deallocation

What it should do

What happens instead

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Rc cycle prevents memory deallocation

What it should do

What happens instead

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