学习rust_day06

Vectors

• 在单一数据结构存储多个值
• 在内存中连续存储（相邻）
• 元素必须是同类型
• Vec来自标准库

例：

fn main() {
    let v: Vec<i32> = Vec::new(); //需要手动标注类型

    let w = vec![1, 2, 3]; //无需手动标注类型

    let mut v = Vec::new();

    //向vec中加入元素
    v.push(1);
    v.push(2);
    v.push(3);

    //引用vec元素
    let third: &i32 = &v[2];

    let third: Option<&i32> = v.get(2);
    match third {
        Some(third) => println!("Get it"),
        None => println!("No way"),
    }

    //遍历vec中的元素
    for n_ref in &v {
        let n_plus_one: i32 = *n_ref + 1;
        println!("{n_plus_one}");
    }

    //在vec中存储不同的元素
    enum S {
        Int(i32),
        Float(f64),
        Text(String)
    }

    let row = vec![S::Int(3), S::Text(String::from("hello")), S::Float(3.14)];

}

---

String

Rust中只存在一种字符串类型：str(&str) 字符串切片。

例：

fn main() {
    //初始化String
    let mut s = String::new();

    let data = "wtf";
    let s = data.to_string();

    let s = "wtf".to_string();

    let s = String::from("wtf");

    //修改或更新String
    let mut s = String::from("foo");
    let s2 = "bar";
    s.push_str(s2);
    println!("{s2}"); //S2仍然可以使用

    //连接String
    let s1 = String::from("Hello ");
    let s2 = String::from("world");
    let s3 = s1 + &s2; //s2后续仍然可以使用

    let s = format!("{s3}-{s2}-{s2}");

    //对String进行切片
    let s4 = &s[0..4];

    //遍历String
    for c in s4.chars() {
        println!("{c}"); //输出字符
    }

    for c in s4.bytes() {
        println!("{c}"); //输出数字
    }

}

---

HashMap

• 存储键值对(K,V)的映射的集合
• Hashing函数
• 通过K来查找

例：

use std::collections::HashMap;

fn main() {
    //创建HashMap
    let mut scores = HashMap::new();
    scores.insert(String::from("Blue"), 10);
    scores.insert(String::from("Red"), 20);
    
    let vec = vec![("Blue", 10), ("Red", 20)];
    let map: HashMap<_, _> = vec.into_iter().collect();

    //访问HashMap的值
    let team_name = String::from("Blue");
    let score = scores.get(&team_name).copied().unwrap_or(0);

    //遍历HashMap
    for (key, value) in &scores {
        println!("{} : {}", key, value);
    }

    //更新HashMap
    scores.insert(String::from("Blue"), 30);
    scores.insert(String::from("Blue"), 35);
    
    for (key, value) in &scores {
        println!("{} : {}", key, value);
    }

    scores.entry(String::from("Yellow")).or_insert(10); //如果不存在键才会插入
    scores.entry(String::from("Blue")).or_insert(50);

    for (key, value) in &scores {
        println!("{} : {}", key, value);
    }

    //基于key原有的值进行更新
    let text = "hello world world wonderful world";
    let mut map = HashMap::new();
    for word in text.split_whitespace() {
        let count = map.entry(word).or_insert(0);
        *count += 1;
    }
    println!("{map:#?}");

}