当运行以下代码时，这些代码来自Rust Book中的练习：

use std::collections::HashMap;

fn main() {
    let mut values = [5, 34, 31, 4, 31, 25, 28, 45, 43, 14];
    values.sort();

    let mut total = 0;
    let mut mode_collection = HashMap::new();
    let mut mode = HashMap::new();

    for value in values.iter() {
        let count = mode_collection.entry(value.clone()).or_insert(0);
        *count += 1;
        total += value;
    };

    for (value, count) in mode_collection.iter() {
        let count_values = mode.entry(count).or_insert(vec![]);
        count_values.push(value.clone());
    }

    let mut largest_count: i32 = 0;
    for count in mode.keys().collect() {
        if count > largest_count {
            largest_count = count;
        }
    }

    println!("The average of the values is {}", total / values.len());
    println!("The median of the values is {}", values[values.len() / 2]);
    println!("The mode of the values is {:?}", mode[&largest_count]);
}

In Rust Playground
我得到一个错误：

error[E0282]: type annotations needed
  --> src\main.rs:24:18
   |
24 |     for count in mode.keys().collect() {
   |                  ^^^^^^^^^^^^^^^^^^^^^ cannot infer type

error: aborting due to previous error

For more information about this error, try `rustc --explain E0282`.
error: could not compile `enums`

To learn more, run the command again with --verbose.

如何避免此错误？
据我所知，类型注解不能添加到for循环中。但是在使用collect()时，类型注解是必需的。当我去掉collect()时，count是&&{Integer}（一个双重借用的整数？），所以largest_count和count变量不能比较。