直接上代码：

use std::collections::HashMap;

// 获取平均数
pub fn get_average_number(vec_numbers:&Vec<i64>) -> Option<f64> {
    if vec_numbers.is_empty() {
        return None;
    }

    let mut result: f64 = 0.0;
    for i in vec_numbers.iter() {
        result += *i as f64;
    }
    
    result = result/vec_numbers.len() as f64;
    return Some(result);
}

// 获取中位数
pub fn get_median_number(vec_numbers:&mut Vec<i64>) -> Option<f64> {
    vec_numbers.sort();
    let len = vec_numbers.len();
    println!("{:?}", vec_numbers);
    match vec_numbers.len()%2 {
        1 => Some(vec_numbers[len/2 as usize] as f64),
        _ => Some((vec_numbers[len/2 as usize - 1] + vec_numbers[len/2 as usize]) as f64/2.0),
    }
}

// 获取众数
pub fn get_mode_number(vec_numbers:&mut Vec<i64>) -> Option<i64> {
    let mut map_numbers: HashMap<i64, i64> = HashMap::new();
    for i in vec_numbers {
        let count = map_numbers.entry(*i).or_insert(0); 
        *count += 1;
    }

    let mut result: i64 = 0;
    let mut value: i64 = 0;
    for (k, v) in &map_numbers {
        if *v >= value {
            value = *v;
            result = *k;
        }
        else {
            continue;
        }
    }

    Some(result)
}

需要注意的是，获取中位数的入参为可变引用，调用后原Vec的顺序会被改变