问题描述
我正在处理 leetcode 问题 #83从排序列表中删除重复项",但我被这个借用检查器问题困住了.
I am working on leetcode problem #83 "Remove Duplicates from Sorted List", but I'm stuck on this borrow checker issue.
ListNode 结构由问题给出,因此无法更改.我已经尝试重组循环和 if 语句,但我还没有找到可行的解决方案.
The ListNode struct is given by the problem so it cannot be changed. I have tried restructuring the loop and if statement, but I haven't found a working solution.
我想做什么:
// Definition for singly-linked list.
#[derive(PartialEq, Eq, Debug)]
pub struct ListNode {
pub val: i32,
pub next: Option<Box<ListNode>>,
}
impl ListNode {
#[inline]
fn new(val: i32) -> Self {
ListNode { next: None, val }
}
}
fn remove_duplicates(mut list: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
let mut cursor = &mut list;
while let Some(c) = cursor.as_mut() {
if let Some(next) = c.next.as_mut() {
if next.val == c.val {
c.next = next.next.take();
continue;
}
}
cursor = &mut c.next;
}
list
}
我得到的错误:
error[E0499]: cannot borrow `*cursor` as mutable more than once at a time
--> src/lib.rs:17:25
|
17 | while let Some(c) = cursor.as_mut() {
| ^^^^^^ mutable borrow starts here in previous iteration of loop
似乎显示相同错误的简化代码:
Simplified code that seems to show the same error:
fn remove_duplicates(mut list: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
let mut cursor = &mut list;
while let Some(c) = cursor.as_mut() {
if c.val > 0 {
cursor = &mut c.next;
}
}
list
}
我不明白为什么在循环的下一次迭代之前没有删除可变借用.这似乎是由有条件地更改游标引起的,但我不明白为什么会阻止借用被删除.
I don't understand why the mutable borrow hasn't been dropped before the next iteration of the loop. It seems to be caused by conditionally changing the cursor, but I don't see why that would prevent the borrow from being dropped.
推荐答案
这是我最终得到的解决方案.在 if 语句中重新分配 cursor
可以解决问题.
Here's the solution I ended up with. Reassigning cursor
in the if statement fixes the problem.
fn remove_duplicates(mut list: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
let mut cursor = list.as_mut();
while let Some(c) = cursor {
if let Some(next) = c.next.as_mut() {
if next.val == c.val {
c.next = next.next.take();
cursor = Some(c);
continue;
}
}
cursor = c.next.as_mut();
}
list
}
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