Rust 编程小技巧(6)

1. 打印字符串

fn main() {
    println!("Hello, world");
    let s = "Rust";
    print!("{}", s);
    println!();
}

Rust 打印主要用宏 print!()、println!()，打印宏的占位符使用 {}。

2. 重复打印字串

有多种方法，比如使用：循环、string.repeat()、vector.join()等等。

fn main() {
    for _ in 0..8 {
        print!("rust");
    }

    println!("\n{}", "rust".repeat(8));

    let s = vec!["rust"; 8];
    println!("{:?}", s);
    println!("{}", s.join(""));
    println!("{}", s.join("."));
}

输出：

rustrustrustrustrustrustrustrust
rustrustrustrustrustrustrustrust
["rust", "rust", "rust", "rust", "rust", "rust", "rust", "rust"]
rustrustrustrustrustrustrustrust
rust.rust.rust.rust.rust.rust.rust.rust

3. 自定义函数

比如，一个整数的平方、绝对值

fn square(x: i32) -> i32 {
    x * x
}

fn abs(x: i32) -> i32 {
    if x < 0 {
        return -x;
    }
    x
}

fn main() {
    let n = square(9);
    println!("{}", n);
    println!("{}", abs(-10));
}

rust 函数的返回关键字 return，在最后的出口可以省略，只需一个表达式（不用分号结尾）。

4. 遍历动态数组

.into_iter() 转迭代器

fn main() {
    let items = vec![11, 22, 33];

    for x in items.clone().into_iter() {
        do_something(x);
    }

    items.clone().into_iter().for_each(|x| do_something(x));

    println!("{:?}", items);
}

fn do_something(n: i64) {
    println!("Number {}", n)
}

输出：

Number 11
Number 22
Number 33
Number 11
Number 22
Number 33
[11, 22, 33]

5. 遍历二维数组

.iter() 创建迭代器

fn main() {
    let vec = vec![vec![1, 2], vec![3, 4], vec![5, 6]];  
    for outer_iter in vec.iter() {  
        for inner_iter in outer_iter.iter() {  
            print!("{} ", inner_iter);  
        }  
    }
    println!();

    vec.iter().for_each(|x| x.iter().for_each(|y| print!("{} ", y)));
    println!();
}

6. 同时遍历索引和值

.enumerate() 枚举

fn main() {
    test1();
    test2();
}

fn test1() {
    let items = ["a", "b", "c"];
    for (i, x) in items.iter().enumerate() {
        println!("Item {} = {}", i, x);
    }
}

fn test2() {
    let items = ["a", "b", "c"];
    items.iter().enumerate().for_each(|(i, x)| {
        println!("Item {} = {}", i, x);
    });
}

7. 检查数组是否包含某个值

代码1：for ... in 遍历

fn contain(list: &[i32], num: i32) {
    let mut flag = false;
    for &i in list {
        if i == num {
            flag = true;
            break;
        }
    }
    if flag {
        println!("{:?} 包含 {}", list, num);
    } else {
        println!("{:?} 不含 {}", list, num);
    }
}
  
fn main() {
    let list = [1, 2, 3];
    let num = 0;
    contain(&list, num);
    let num = 2;
    contain(&list, num);
}

代码2：迭代器 + any()方法

fn contain(list: &[i32], num: i32) {
    let flag = list.iter().any(|&item| item == num);
    if flag {
        println!("{:?} 包含 {}", list, num);
    } else {
        println!("{:?} 不含 {}", list, num);
    }
}
  
fn main() {
    let list = [1, 2, 3];
    let num = 0;
    contain(&list, num);
    let num = 2;
    contain(&list, num);
}

代码3：直接用包含方法 contains()

fn contain(list: &[i32], num: i32) {  
    if list.contains(&num) {  
        println!("{:?} 包含 {}", list, num);  
    } else {  
        println!("{:?} 不含 {}", list, num);  
    }  
}  
  
fn main() {  
    let list = [1, 2, 3];  
    let num = 0;  
    contain(&list, num);  
    let num = 2;  
    contain(&list, num);  
}

输出：

[1, 2, 3] 不含 0
[1, 2, 3] 包含 2

8. 二维矩阵中查找某个值

fn search<T: Eq>(m: &Vec<Vec<T>>, x: &T) -> Option<(usize, usize)> {
    for (i, row) in m.iter().enumerate() {
        for (j, col) in row.iter().enumerate() {
            if *col == *x {
                return Some((i, j));
            }
        }
    }
    None
}

fn main() {
    let v = vec![
        vec![1, 2, 3],
        vec![4, 5, 6],
        vec![7, 8, 9],
    ];
    println!("{:?}", search(&v, &6));
    println!("{:?}", search(&v, &0));
}

输出：

Some((1, 2))
None