值移动到这里，在循环的前一次迭代中 [英] Value moved here, in previous iteration of loop

问题描述

这是我为 LeetCode:添加两个数字

This is what I wrote for LeetCode: Add Two Numbers

//2. Add Two Numbers
// Definition for singly-linked list.
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct ListNode {
    pub val: i32,
    pub next: Option<Box<ListNode>>,
}

impl ListNode {
    #[inline]
    fn new(val: i32) -> Self {
        ListNode { next: None, val }
    }
}

struct Solution;

impl Solution {
    pub fn list_to_num(ls: &Option<Box<ListNode>>) -> i64 {
        let mut vec = vec![];
        let mut head = ls;

        while let Some(node) = head {
            vec.push(node.val);
            head = &node.next;
        }

        vec.reverse();

        let mut num = 0i64;

        for x in vec {
            num *= 10;
            num += x as i64;
        }

        num
    }

    pub fn num_to_list(num: i64) -> Option<Box<ListNode>> {
        let num_str = num.to_string();
        let vec = num_str
            .chars()
            .map(|x| x.to_digit(10).unwrap() as i32)
            .collect::<Vec<_>>();

        let mut res = None;
        for x in vec {
            let mut one = ListNode::new(x);
            one.next = res;
            res = Some(Box::new(one));
        }

        res
    }

    pub fn add_two_numbers(
        l1: Option<Box<ListNode>>,
        l2: Option<Box<ListNode>>,
    ) -> Option<Box<ListNode>> {
        let mut vec = vec![] as Vec<i32>;
        let mut step = 0;
        let mut left = l1;
        let mut right = l2;
        loop {
            match (left, right) {
                (None, None) => {
                    if step != 0 {
                        vec.push(step);
                    }
                    break;
                }
                (Some(leftN), None) => {
                    let curr = leftN.val + step;
                    if curr >= 10 {
                        vec.push(curr - 10);
                        step = 1
                    } else {
                        vec.push(curr);
                        step = 0
                    }
                    left = leftN.next
                }
                (None, Some(rightN)) => {
                    let curr = rightN.val + step;
                    if curr >= 10 {
                        vec.push(curr - 10);
                        step = 1
                    } else {
                        vec.push(curr);
                        step = 0
                    }
                    right = rightN.next
                }
                (Some(leftN), Some(rightN)) => {
                    let curr = leftN.val + rightN.val + step;
                    if curr >= 10 {
                        vec.push(curr - 10);
                        step = 1
                    } else {
                        vec.push(curr);
                        step = 0
                    }
                    right = rightN.next;
                    left = leftN.next
                }
            }
        }

        vec.reverse();

        let mut res = None;

        for x in vec {
            let mut next = ListNode::new(x);
            next.next = res;
            res = Some(Box::new(next));
        }
        res
    }
}

fn main() {
    let list1 = Solution::num_to_list(9);
    let list2 = Solution::num_to_list(991);
    println!("list1 {:?}", list1);
    println!("list2 {:?}", list2);
    let res = Solution::add_two_numbers(list1, list2);
    println!("summed {:#?}", res);
}

出现编译错误

error[E0382]: use of moved value: `left`
  --> src/main.rs:66:20
   |
63 |         let mut left = l1;
   |             -------- move occurs because `left` has type `std::option::Option<std::boxed::Box<ListNode>>`, which does not implement the `Copy` trait
...
66 |             match (left, right) {
   |                    ^^^^ value moved here, in previous iteration of loop

error[E0382]: use of moved value: `right`
  --> src/main.rs:66:26
   |
64 |         let mut right = l2;
   |             --------- move occurs because `right` has type `std::option::Option<std::boxed::Box<ListNode>>`, which does not implement the `Copy` trait
65 |         loop {
66 |             match (left, right) {
   |                          ^^^^^ value moved here, in previous iteration of loop

我认为每次迭代都是独立的，如果该值是由前一次迭代借用的，则应该在本次"迭代中返回.

I think each iteration is independent, and if the value is borrowed by a previous iteration, it should be returned in "this" iteration.

如果我将 match (left, right) { 替换为 match (left.clone(), right.clone()) {，代码编译，但它可能会消耗比必要更多的内存.什么是使其编译并节省内存的更好方法?

If I replace match (left, right) { with match (left.clone(), right.clone()) {, the code compiles, but it might consume more memory than necessary. What is the better way to make it compile and be memory economical?

推荐答案

您不是在借用节点，而是在移动它们.

You're not borrowing the nodes, you're moving them.

为了使用引用，你应该替换

In order to use references, you should replace

let mut left = l1;
let mut right = l2;

与

let mut left = &l1;
let mut right = &l2;

然后再

right = rightN.next;

与

right = &rightN.next;

等

游乐场

这篇关于值移动到这里，在循环的前一次迭代中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！