161. Multiply all the elements of a list
Multiply all the elements of the list elements by a constant c
将list中的每个元素都乘以一个数
package main import ( "fmt" ) func main() { const c = 5.5 elements := []float64{2, 4, 9, 30} fmt.Println(elements) for i := range elements { elements[i] *= c } fmt.Println(elements) }
[2 4 9 30] [11 22 49.5 165]
fn main() { let elements: Vec<f32> = vec![2.0, 3.5, 4.0]; let c = 2.0; let elements = elements.into_iter().map(|x| c * x).collect::<Vec<_>>(); println!("{:?}", elements); }
162. Execute procedures depending on options
execute bat if b is a program option and fox if f is a program option.
根据选项执行程序
package main import ( "flag" "fmt" "os" ) func init() { // Just for testing in the Playground, let's simulate // the user called this program with command line // flags -f and -b os.Args = []string{"program", "-f", "-b"} } var b = flag.Bool("b", false, "Do bat") var f = flag.Bool("f", false, "Do fox") func main() { flag.Parse() if *b { bar() } if *f { fox() } fmt.Println("The end.") } func bar() { fmt.Println("BAR") } func fox() { fmt.Println("FOX") }
BAR FOX The end.
if let Some(arg) = ::std::env::args().nth(1) { if &arg == "f" { fox(); } else if &arg = "b" { bat(); } else { eprintln!("invalid argument: {}", arg), } } else { eprintln!("missing argument"); }
or
if let Some(arg) = ::std::env::args().nth(1) { match arg.as_str() { "f" => fox(), "b" => box(), _ => eprintln!("invalid argument: {}", arg), }; } else { eprintln!("missing argument"); }
163. Print list elements by group of 2
Print all the list elements, two by two, assuming list length is even.
两个一组打印数组元素
package main import ( "fmt" ) func main() { list := []string{"a", "b", "c", "d", "e", "f"} for i := 0; i+1 < len(list); i += 2 { fmt.Println(list[i], list[i+1]) } }
a b c d e f
fn main() { let list = [1,2,3,4,5,6]; for pair in list.chunks(2) { println!("({}, {})", pair[0], pair[1]); } }
(1, 2) (3, 4) (5, 6)
164. Open URL in default browser
Open the URL s in the default browser. Set boolean b to indicate whether the operation was successful.
在默认浏览器中打开链接
import "github.com/skratchdot/open-golang/open" b := open.Start(s) == nil
or
func openbrowser(url string) { var err error switch runtime.GOOS { case "linux": err = exec.Command("xdg-open", url).Start() case "windows": err = exec.Command("rundll32", "url.dll,FileProtocolHandler", url).Start() case "darwin": err = exec.Command("open", url).Start() default: err = fmt.Errorf("unsupported platform") } if err != nil { log.Fatal(err) } }
use webbrowser; webbrowser::open(s).expect("failed to open URL");
165. Last element of list
Assign to variable x the last element of list items.
列表中的最后一个元素
package main import ( "fmt" ) func main() { items := []string{ "what", "a", "mess" } x := items[len(items)-1] fmt.Println(x) }
fn main() { let items = vec![5, 6, 8, -20, 9, 42]; let x = items[items.len()-1]; println!("{:?}", x); }
or
fn main() { let items = [5, 6, 8, -20, 9, 42]; let x = items.last().unwrap(); println!("{:?}", x); }
166. Concatenate two lists
Create list ab containing all the elements of list a, followed by all elements of list b.
连接两个列表
package main import ( "fmt" ) func main() { a := []string{"The ", "quick "} b := []string{"brown ", "fox "} ab := append(a, b...) fmt.Printf("%q", ab) }
or
package main import ( "fmt" ) func main() { type T string a := []T{"The ", "quick "} b := []T{"brown ", "fox "} var ab []T ab = append(append(ab, a...), b...) fmt.Printf("%q", ab) }
or
package main import ( "fmt" ) func main() { type T string a := []T{"The ", "quick "} b := []T{"brown ", "fox "} ab := make([]T, len(a)+len(b)) copy(ab, a) copy(ab[len(a):], b) fmt.Printf("%q", ab) }
fn main() { let a = vec![1, 2]; let b = vec![3, 4]; let ab = [a, b].concat(); println!("{:?}", ab); }
167. Trim prefix
Create string t consisting of string s with its prefix p removed (if s starts with p).
移除前缀
package main import ( "fmt" "strings" ) func main() { s := "café-society" p := "café" t := strings.TrimPrefix(s, p) fmt.Println(t) }
fn main() { { let s = "pre_thing"; let p = "pre_"; let t = s.trim_start_matches(p); println!("{}", t); } { // Warning: trim_start_matches removes several leading occurrences of p, if present. let s = "pre_pre_thing"; let p = "pre_"; let t = s.trim_start_matches(p); println!("{}", t); } }
thing thing
or
fn main() { let s = "pre_pre_thing"; let p = "pre_"; let t = if s.starts_with(p) { &s[p.len()..] } else { s }; println!("{}", t); }
or
fn main() { { let s = "pre_thing"; let p = "pre_"; let t = s.strip_prefix(p).unwrap_or_else(|| s); println!("{}", t); } { // If prefix p is repeated in s, it is removed only once by strip_prefix let s = "pre_pre_thing"; let p = "pre_"; let t = s.strip_prefix(p).unwrap_or_else(|| s); println!("{}", t); } }
thing pre_thing
168. Trim suffix
Create string t consisting of string s with its suffix w removed (if s ends with w).
移除后缀
package main import ( "fmt" "strings" ) func main() { s := "café-society" w := "society" t := strings.TrimSuffix(s, w) fmt.Println(t) }
fn main() { let s = "thing_suf"; let w = "_suf"; let t = s.trim_end_matches(w); println!("{}", t); let s = "thing"; let w = "_suf"; let t = s.trim_end_matches(w); // s does not end with w, it is left intact println!("{}", t); let s = "thing_suf_suf"; let w = "_suf"; let t = s.trim_end_matches(w); // removes several occurrences of w println!("{}", t); }
thing thing thing
or
fn main() { let s = "thing_suf"; let w = "_suf"; let t = s.strip_suffix(w).unwrap_or(s); println!("{}", t); let s = "thing"; let w = "_suf"; let t = s.strip_suffix(w).unwrap_or(s); // s does not end with w, it is left intact println!("{}", t); let s = "thing_suf_suf"; let w = "_suf"; let t = s.strip_suffix(w).unwrap_or(s); // only 1 occurrence of w is removed println!("{}", t); }
thing thing thing_suf
169. String length
Assign to integer n the number of characters of string s. Make sure that multibyte characters are properly handled. n can be different from the number of bytes of s.
字符串长度
package main import "fmt" import "unicode/utf8" func main() { s := "Hello, 世界" n := utf8.RuneCountInString(s) fmt.Println(n) }
fn main() { let s = "世界"; let n = s.chars().count(); println!("{} characters", n); }
170. Get map size
Set n to the number of elements stored in mymap.
This is not always equal to the map capacity.
获取map的大小
package main import "fmt" func main() { mymap := map[string]int{"a": 1, "b": 2, "c": 3} n := len(mymap) fmt.Println(n) }
use std::collections::HashMap; fn main() { let mut mymap: HashMap<&str, i32> = [("one", 1), ("two", 2)].iter().cloned().collect(); mymap.insert("three", 3); let n = mymap.len(); println!("mymap has {:?} entries", n); }
