21. Swap values
交换变量a和b的值
a, b = b, a
package main import "fmt" func main() { a := 3 b := 10 a, b = b, a fmt.Println(a) fmt.Println(b) }
10 3
fn main() { let a = 3; let b = 10; let (a, b) = (b, a); println!("a: {a}, b: {b}", a=a, b=b); }
输出
a: 10, b: 3
or
fn main() { let (a, b) = (12, 42); println!("a = {}, b = {}", a, b); let (a, b) = (b, a); println!("a = {}, b = {}", a, b); }
输出
a = 12, b = 42 a = 42, b = 12
22. Convert string to integer
将字符串转换为整型
import "strconv" i, err := strconv.Atoi(s)
package main import ( "fmt" "reflect" "strconv" ) func main() { // create a string s := "123" fmt.Println(s) fmt.Println("type:", reflect.TypeOf(s)) // convert string to int i, err := strconv.Atoi(s) if err != nil { panic(err) } fmt.Println(i) fmt.Println("type:", reflect.TypeOf(i)) }
123 type: string 123 type: int
or
import "strconv" i, err := strconv.ParseInt(s, 10, 0)
package main import ( "fmt" "reflect" "strconv" ) func main() { s := "123" fmt.Println("s is", reflect.TypeOf(s), s) i, err := strconv.ParseInt(s, 10, 0) if err != nil { panic(err) } fmt.Println("i is", reflect.TypeOf(i), i) }
s is string 123 i is int64 123
fn main() { // This prints 123 let mut s = "123"; let mut i = s.parse::<i32>().unwrap(); println!("{:?}", i); // This panics s = "12u3"; i = s.parse::<i32>().unwrap(); println!("{:?}", i); }
输出
123 thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: InvalidDigit }', src/libcore/result.rs:860 note: Run with `RUST_BACKTRACE=1` for a backtrace.
or
fn main() { let mut s = "123"; let mut i: i32 = s.parse().unwrap_or(0); println!("{:?}", i); s = "12u3"; i = s.parse().unwrap_or(0); println!("{:?}", i); }
输出
123 0
or
fn main() { let mut s = "123"; let mut i = match s.parse::<i32>() { Ok(i) => i, Err(_e) => -1, }; println!("{:?}", i); s = "12u3"; i = match s.parse::<i32>() { Ok(i) => i, Err(_e) => -1, }; println!("{:?}", i); }
输出
123 -1
23. Convert real number to string with 2 decimal places
Given a real number x, create its string representation s with 2 decimal digits following the dot.
给定一个实数，小数点后保留两位小数
package main import "fmt" func main() { x := 3.14159 s := fmt.Sprintf("%.2f", x) fmt.Println(s) }
输出
fn main() { let x = 42.1337; let s = format!("{:.2}", x); println!("{}", s); }
输出
42.13
24. Assign to string the japanese word ネコ
Declare a new string s and initialize it with the literal value "ネコ" (which means "cat" in japanese)
声明一个新的字符串s，并用文字值“ネコ”初始化它(在日语中是“cat”的意思)
package main import "fmt" func main() { s := "ネコ" fmt.Println(s) }
fn main() { let s = "ネコ"; println!("{}", s); }
25. Send a value to another thread
Share the string value "Alan" with an existing running process which will then display "Hello, Alan"
将字符串值“Alan”与现有的正在运行的进程共享，该进程将显示“你好，Alan”
ch <- "Alan"
package main import ( "fmt" "time" ) func main() { ch := make(chan string) go func() { v := <-ch fmt.Printf("Hello, %v\n", v) }() ch <- "Alan" // Make sure the non-main goroutine had the chance to finish. time.Sleep(time.Second) }
The receiver goroutine blocks reading the string channel ch. The current goroutine sends the value to ch. A goroutine is like a thread, but more lightweight.
use std::thread; use std::sync::mpsc::channel; fn main() { let (send, recv) = channel(); let handle = thread::spawn(move || loop { let msg = recv.recv().unwrap(); println!("Hello, {:?}", msg); }); send.send("Alan").unwrap(); handle.join().unwrap(); }
输出 Hello, "Alan"
26. Create a 2-dimensional array
Declare and initialize a matrix x having m rows and n columns, containing real numbers.
创建一个二维数组
声明并初始化一个有m行n列的矩阵x，包含实数。
const m, n = 3, 4 var x [m][n]float64
package main import "fmt" func main() { const m, n = 3, 4 var x [m][n]float64 x[1][2] = 8 fmt.Println(x) }
or
package main import "fmt" func main() { x := make2D(2, 3) x[1][1] = 8 fmt.Println(x) } func make2D(m, n int) [][]float64 { buf := make([]float64, m*n) x := make([][]float64, m) for i := range x { x[i] = buf[:n:n] buf = buf[n:] } return x }
fn main() { const M: usize = 4; const N: usize = 6; let x = vec![vec![0.0f64; N]; M]; println!("{:#?}", x); }
输出
[ [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, ], [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, ], [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, ], [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, ], ]
fn main() { const M: usize = 3; const N: usize = 4; let mut x = [[0.0; N] ; M]; x[1][3] = 5.0; println!("{:#?}", x); }
输出
[ [ 0.0, 0.0, 0.0, 0.0, ], [ 0.0, 0.0, 0.0, 5.0, ], [ 0.0, 0.0, 0.0, 0.0, ], ]
27. Create a 3-dimensional array
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.
创建一个三维数组
声明并初始化一个三维数组x，它有m，n，p维边界，并且包含实数。
const m, n, p = 2, 2, 3 var x [m][n][p]float64
package main import "fmt" func main() { const m, n, p = 2, 2, 3 var x [m][n][p]float64 x[1][0][2] = 9 // Value of x fmt.Println(x) // Type of x fmt.Printf("%T", x) }
[[[0 0 0] [0 0 0]] [[0 0 9] [0 0 0]]] [2][2][3]float64
or
func make3D(m, n, p int) [][][]float64 { buf := make([]float64, m*n*p) x := make([][][]float64, m) for i := range x { x[i] = make([][]float64, n) for j := range x[i] { x[i][j] = buf[:p:p] buf = buf[p:] } } return x }
package main import "fmt" func main() { x := make3D(2, 2, 3) x[1][0][2] = 9 fmt.Println(x) } func make3D(m, n, p int) [][][]float64 { buf := make([]float64, m*n*p) x := make([][][]float64, m) for i := range x { x[i] = make([][]float64, n) for j := range x[i] { x[i][j] = buf[:p:p] buf = buf[p:] } } return x }
[[[0 0 0] [0 0 0]] [[0 0 9] [0 0 0]]]
fn main() { let m = 4; let n = 6; let p = 2; let x = vec![vec![vec![0.0f64; p]; n]; m]; println!("{:#?}", x); }
输出
[ [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], ]
fn main() { const M: usize = 4; const N: usize = 6; const P: usize = 2; let x = [[[0.0f64; P]; N]; M]; println!("{:#?}", x); }
输出
[ [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], [ [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], [ 0.0, 0.0, ], ], ]
28. Sort by a property
Sort elements of array-like collection items in ascending order of x.p, where p is a field of the type Item of the objects in items.
按x->p的升序对类似数组的集合项的元素进行排序，其中p是项中对象的项类型的字段。
package main import "fmt" import "sort" type Item struct { label string p int lang string } type ItemPSorter []Item func (s ItemPSorter) Len() int { return len(s) } func (s ItemPSorter) Less(i, j int) bool { return s[i].p < s[j].p } func (s ItemPSorter) Swap(i, j int) { s[i], s[j] = s[j], s[i] } func sortItems(items []Item) { sorter := ItemPSorter(items) sort.Sort(sorter) } func main() { items := []Item{ {"twelve", 12, "english"}, {"six", 6, "english"}, {"eleven", 11, "english"}, {"zero", 0, "english"}, {"two", 2, "english"}, } fmt.Println("Unsorted: ", items) sortItems(items) fmt.Println("Sorted: ", items) }
Unsorted: [{twelve 12 english} {six 6 english} {eleven 11 english} {zero 0 english} {two 2 english}] Sorted: [{zero 0 english} {two 2 english} {six 6 english} {eleven 11 english} {twelve 12 english}]
or
package main import "fmt" import "sort" type Item struct { label string p int lang string } func main() { items := []Item{ {"twelve", 12, "english"}, {"six", 6, "english"}, {"eleven", 11, "english"}, {"zero", 0, "english"}, {"two", 2, "english"}, } fmt.Println("Unsorted: ", items) less := func(i, j int) bool { return items[i].p < items[j].p } sort.Slice(items, less) fmt.Println("Sorted: ", items) }
Unsorted: [{twelve 12 english} {six 6 english} {eleven 11 english} {zero 0 english} {two 2 english}] Sorted: [{zero 0 english} {two 2 english} {six 6 english} {eleven 11 english} {twelve 12 english}]
#[derive(Debug)] struct Foo { p: i32, } fn main() { let mut items = vec![Foo { p: 3 }, Foo { p: 1 }, Foo { p: 2 }, Foo { p: 4 }]; items.sort_by(|a, b| a.p.cmp(&b.p)); println!("{:?}", items); }
输出
[Foo { p: 1 }, Foo { p: 2 }, Foo { p: 3 }, Foo { p: 4 }]
or
#[derive(Debug)] struct Foo { p: i32, } fn main() { let mut items = vec![Foo { p: 3 }, Foo { p: 1 }, Foo { p: 2 }, Foo { p: 4 }]; items.sort_by_key(|x| x.p); println!("{:?}", items); }
输出
[Foo { p: 1 }, Foo { p: 2 }, Foo { p: 3 }, Foo { p: 4 }]
29. Remove item from list, by its index
Remove i-th item from list items. This will alter the original list or return a new list, depending on which is more idiomatic. Note that in most languages, the smallest valid value for i is 0.
从列表项中删除第I项。 这将改变原来的列表或返回一个新的列表，这取决于哪个更习惯。 请注意，在大多数语言中，I的最小有效值是0。
package main import ( "fmt" ) func main() { items := []string{"a", "b", "c", "d", "e", "f"} fmt.Println(items) i := 2 items = append(items[:i], items[i+1:]...) fmt.Println(items) }
[a b c d e f] [a b d e f]
or
copy(items[i:], items[i+1:]) items[len(items)-1] = nil items = items[:len(items)-1]
fn main() { let mut v = vec![1, 2, 3]; assert_eq!(v.remove(1), 2); assert_eq!(v, [1, 3]); }
30. Parallelize execution of 1000 independent tasks
Launch the concurrent execution of procedure f with parameter i from 1 to 1000. Tasks are independent and f(i) doesn't return any value. Tasks need not run all at the same time, so you may use a pool.
用参数I从1到1000启动程序f的并发执行。 任务是独立的，f(i)不返回值。 任务不需要同时运行，所以可以使用pools
import "sync" wg := sync.WaitGroup{} wg.Add(1000) for i := 1; i <= 1000; i++ { go func(j int) { f(j) wg.Done() }(i) } wg.Wait()
package main import ( "fmt" "math/rand" "time" ) func f(i int) { d := rand.Int() % 10000 time.Sleep(time.Duration(d)) fmt.Printf("Hello %v\n", i) } func main() { for i := 1; i <= 1000; i++ { go f(i) } time.Sleep(4 * time.Second) }
use std::thread; fn main() { let threads: Vec<_> = (0..1000).map(|i| thread::spawn(move || f(i))).collect(); for thread in threads { thread.join(); } } fn f(i: i32) { println!("{}", i); }
or
extern crate rayon; use rayon::prelude::*; fn main() { (0..1000).into_par_iter().for_each(f); } fn f(i: i32) { println!("{}", i); }
