遍历BST时借入的临时值下降

如何解决遍历BST时借入的临时值下降

use std::{cell::RefCell,rc::Rc};

#[derive(Debug,PartialEq,Eq)]
pub struct TreeNode {
    pub val: i32,pub left: Option<Rc<RefCell<TreeNode>>>,pub right: Option<Rc<RefCell<TreeNode>>>,}

fn find_min(mut node: &Option<Rc<RefCell<TreeNode>>>) -> i32 {
    while node.as_ref().unwrap().borrow().left.is_some() {
        node = &node.as_ref().unwrap().borrow().left;
    }
    node.as_ref().unwrap().borrow().val
}

error[E0716]: temporary value dropped while borrowed
  --> src/lib.rs:12:17
   |
10 | fn find_min(mut node: &Option<Rc<RefCell<TreeNode>>>) -> i32 {
   |                       - let's call the lifetime of this reference `'1`
11 |     while node.as_ref().unwrap().borrow().left.is_some() {
12 |         node = &node.as_ref().unwrap().borrow().left;
   |         --------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^------ temporary value is freed at the end of this statement
   |         |       |
   |         |       creates a temporary which is freed while still in use
   |         assignment requires that borrow lasts for `'1`

TreeNode已给出，无法更改。

我了解为什么会收到错误，但不知道如何解决。

解决方法

更新：

使用Rc作为参数看起来更好：

use std::rc::Rc;

#[derive(Debug,PartialEq,Eq)]
pub struct TreeNode {
    pub val: i32,pub left: Option<Rc<TreeNode>>,pub right: Option<Rc<TreeNode>>,}

pub fn find_min(mut current: Rc<TreeNode>) -> i32 {
    while current.left.is_some() {
        current = Rc::clone(current.left.as_ref().unwrap());
    }
    current.val
}

fn main() {
    let left_child = TreeNode {
        val: 1,left: None,right: None,};
    let root = TreeNode {
        val: 6,left: Some(Rc::new(left_child)),};
    println!("min: {}",find_min(Rc::new(root)));
}

---

RefCell和mut东西对我来说似乎多余？

那：

use std::rc::Rc;

#[derive(Debug,}

pub fn find_min(root: &TreeNode) -> i32 {
    let mut current = Rc::new(root);
    while current.left.is_some() {
        current = Rc::new(current.left.as_ref().unwrap());
    }
    current.val
}

,

根据this answer编写我的解决方案：

fn find_min(node: &Option<Rc<RefCell<TreeNode>>>) -> i32 {
    let mut curr = node.as_ref().unwrap().clone();
    while curr.borrow().left.is_some() {
        let tmp = curr.borrow().left.as_ref().unwrap().clone();
        curr = tmp;
    }
    let res = curr.borrow().val;
    res
}

这两个临时变量看起来都不好，但这就是事实。