让人抓狂的 Rust

刚看 Rust 没几天，想着去 leetcode 上练练，找到这么一个题

80. 删除排序数组中的重复项 II

答案很简单，Java 代码答案如下

class Solution {
    public int removeDuplicates(int[] nums) {
        int i = 0;
        for (int n : nums)
            if (i < 2 || n > nums[i-2])
                nums[i++] = n;
        return i;
    }
}

很简单吧，也看了几天 Rust 语法了，直接上

fn remove_duplicates(nums: μ Vec<i32>) -> i32 {
    let mut i = 0;
    for x in nums {
        if i < 2 || x > nums[i-2] {
            nums[i] = x;  
        }
        i++;
    }
    return i;
}

这也太简单了，然而。。。

$ cargo run                                                                                                                                       101 ↵
   Compiling demo v0.1.0 (/Users/tiangaoshi/rust/demo)
error: expected expression, found `+`
  --> src/main.rs:14:11
   |
14 |         i++;
   |           ^ expected expression

error[E0308]: mismatched types
  --> src/main.rs:11:25
   |
11 |         if i < 2 || x > nums[i-2] {
   |                         ^^^^^^^^^
   |                         |
   |                         expected `μ i32`, found `i32`
   |                         help: consider mutably borrowing here: `μ nums[i-2]`

error[E0308]: mismatched types
  --> src/main.rs:12:23
   |
12 |             nums[i] = x;  
   |                       ^
   |                       |
   |                       expected `i32`, found `μ i32`
   |                       help: consider dereferencing the borrow: `*x`

error[E0308]: mismatched types
  --> src/main.rs:16:12
   |
8  | fn remove_duplicates(nums: μ Vec<i32>) -> i32 {
   |                                              --- expected `i32` because of return type
...
16 |     return i;
   |            ^ expected `i32`, found `usize`
   |
help: you can convert an `usize` to `i32` and panic if the converted value wouldn't fit
   |
16 |     return i.try_into().unwrap();
   |            ^^^^^^^^^^^^^^^^^^^^^

WTF??? 这么多错误， let mut 不是变量吗，nums 不是数组吗，为啥？

没办法，碰到问题解决问题，

第一个最简单，不支持 ++, 那就 i += 1;

第二个没看懂啥意思，大概是不可变，加一行 let a = i - 2;

第三个有提示了 nums[i] = *x;

最后一个应该是类型错误

fn remove_duplicates(nums: μ Vec<i32>) -> i32 {
    let mut i = 0;
    for x in nums {
        let a = i - 2;
        if i < 2 || *x > nums[a] {
            nums[i] = *x;  
        }
        i += 1;
    }
    return i as i32;
}

gogogo~~~~

╰─$ cargo run                                                                                                                                       101 ↵
   Compiling demo v0.1.0 (/Users/tiangaoshi/rust/demo)
error[E0382]: borrow of moved value: `nums`
  --> src/main.rs:12:26
   |
8  | fn remove_duplicates(nums: μ Vec<i32>) -> i32 {
   |                      ---- move occurs because `nums` has type `μ std::vec::Vec<i32>`, which does not implement the `Copy` trait
9  |     let mut i = 0;
10 |     for x in nums {
   |              ----
   |              |
   |              value moved here
   |              help: consider borrowing to avoid moving into the for loop: `#`
11 |         let a = i - 2;
12 |         if i < 2 || *x > nums[a] {
   |                          ^^^^ value borrowed here after move

error: aborting due to previous error

我真是黑人问号脸了，什么鬼啊

此处省去几天时间的各种尝试和查阅文档，

甚至仔仔细细读了 <<Rust 编程之道 >> 前面几章，

中间还找到了一个仓库 https://github.com/aylei/leetcode-rust ，直接去翻 80

https://github.com/aylei/leetcode-rust/blob/master/src/solution/s0080_remove_duplicates_from_sorted_array_ii.rs

oh shit~
 

今天综合几天的经验，终于尝试搞出了一个能过的版本

fn remove_duplicates(nums: μ Vec<i32>) -> i32 {
    let mut i = 0;
    let list = nums.clone();
    for x in list {
        if i < 2 {
            let a = i;
            nums[a] = x;
            i += 1;
        } else {
            let a = i;
            let b = i - 2;
            if x > nums[b] {
                nums[a] = x;
                i += 1;
            }
        }
    }
    return i as i32;
}

我真的是醉了，这是个什么鬼语言，好歹我也是写过 C 玩过汇编单片机，C++ 入过门，N 年 Java， 一年 Golang 滚过， Kotlin 爽过，中间还掺杂 Elixir Swift 认知的职业搬砖工，这写第一个算法题就玩我这么久，坑啊

只能说自己菜了，果然老人言说得对，一上来就写代码肯定会栽跟头的

Rust 肯定是值得学习的，看看人家 actix，简直是一骑绝尘

TechEmpower Framework Benchmarks Performance comparison of a wide spectrum of web application frameworks and platforms using community-contributed test implementations. www.techempower.com

学无止境，目测最最后一版也只是能过而已，肯定有更精炼的写法，手动捂脸，🤦🤦🤦

最后附上一个此题的提交记录，同一套算法

第二天

感觉好像又理解了些东西，又写了一版，好看多了，舒服

impl Solution {
    fn remove_duplicates(nums: μ Vec<i32>) -> i32 {
        let mut ans = 2;
        let size = nums.len();
        for i in 2..size {
            let a = ans - 2;
            if nums[a] < nums[i] {
                nums[ans] = nums[i];
                ans += 1;
            }
        }
        return ans as i32;
    }
}

觉得学语言其实是在学模式，解决一个问题有千万种方法，不通的方法对应的也是不通的效率，开发效率跟运行效率就像鱼跟熊掌，enmmm，小孩子才做选择，我都要