221. Remove all non-digits characters
Create string t from string s, keeping only digit characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
删除所有非数字字符
package main import ( "fmt" "regexp" ) func main() { s := `height="168px"` re := regexp.MustCompile("[^\\d]") t := re.ReplaceAllLiteralString(s, "") fmt.Println(t) }
fn main() { let t: String = "Today is the 14th of July" .chars() .filter(|c| c.is_digit(10)) .collect(); dbg!(t); }
222. Find first index of an element in list
Set i to the first index in list items at which the element x can be found, or -1 if items does not contain x.
在列表中查找元素的第一个索引
package main import ( "fmt" ) func main() { items := []string{"huey", "dewey", "louie"} x := "dewey" i := -1 for j, e := range items { if e == x { i = j break } } fmt.Printf("Found %q at position %d in %q", x, i, items) }
fn main() { let items = ['A', '🎂', '㍗']; let x = '💩'; match items.iter().position(|y| *y == x) { Some(i) => println!("Found {} at position {}.", x, i), None => println!("There is no {} in the list.", x), } }
or
fn main() { let items = [42, -3, 12]; { let x = 12; let i = items.iter().position(|y| *y == x).map_or(-1, |n| n as i32); println!("{} => {}", x, i) } { let x = 13; let i = items.iter().position(|y| *y == x).map_or(-1, |n| n as i32); println!("{} => {}", x, i) } }
12 => 2 13 => -1
223. for else loop
Loop through list items checking a condition. Do something else if no matches are found.
A typical use case is looping through a series of containers looking for one that matches a condition. If found, an item is inserted; otherwise, a new container is created.
These are mostly used as an inner nested loop, and in a location where refactoring inner logic into a separate function reduces clarity.
for else循环
package main import ( "fmt" ) func main() { items := []string{"foo", "bar", "baz", "qux"} for _, item := range items { if item == "baz" { fmt.Println("found it") goto forelse } } { fmt.Println("never found it") } forelse: }
fn main() { let items: &[&str] = &["foo", "bar", "baz", "qux"]; let mut found = false; for item in items { if item == &"baz" { println!("found it"); found = true; break; } } if !found { println!("never found it"); } }
or
fn main() { let items: &[&str] = &["foo", "bar", "baz", "qux"]; if let None = items.iter().find(|&&item| item == "rockstar programmer") { println!("NotFound"); }; }
or
fn main() { let items: &[&str] = &["foo", "bar", "baz", "qux"]; items .iter() .find(|&&item| item == "rockstar programmer") .or_else(|| { println!("NotFound"); Some(&"rockstar programmer") }); }
224. Add element to the beginning of the list
Insert element x at the beginning of list items.
将元素添加到列表的开头
package main import ( "fmt" ) type T int func main() { items := []T{42, 1337} var x T = 7 items = append([]T{x}, items...) fmt.Println(items) }
or
package main import ( "fmt" ) type T int func main() { items := []T{42, 1337} var x T = 7 items = append(items, x) copy(items[1:], items) items[0] = x fmt.Println(items) }
use std::collections::VecDeque; fn main() { let mut items = VecDeque::new(); items.push_back(22); items.push_back(33); let x = 11; items.push_front(x); println!("{:?}", items); }
225. Declare and use an optional argument
Declare an optional integer argument x to procedure f, printing out "Present" and its value if it is present, "Not present" otherwise
声明并使用可选参数
package main func f(x ...int) { if len(x) > 0 { println("Present", x[0]) } else { println("Not present") } } func main() { f() f(1) }
Go does not have optional arguments, but to some extend, they can be mimicked with a variadic parameter. x is a variadic parameter, which must be the last parameter for the function f. Strictly speaking, x is a list of integers, which might have more than one element. These additional elements are ignored.
Not present Present 1
fn f(x: Option<()>) { match x { Some(x) => println!("Present {}", x), None => println!("Not present"), } }
226. Delete last element from list
Remove the last element from list items.
从列表中删除最后一个元素
package main import ( "fmt" ) func main() { items := []string{"banana", "apple", "kiwi"} fmt.Println(items) items = items[:len(items)-1] fmt.Println(items) }
[banana apple kiwi] [banana apple]
fn main() { let mut items = vec![11, 22, 33]; items.pop(); println!("{:?}", items); }
227. Copy list
Create new list y containing the same elements as list x.
Subsequent modifications of y must not affect x (except for the contents referenced by the elements themselves if they contain pointers).
复制列表
package main import ( "fmt" ) func main() { type T string x := []T{"Never", "gonna", "shower"} y := make([]T, len(x)) copy(y, x) y[2] = "give" y = append(y, "you", "up") fmt.Println(x) fmt.Println(y) }
[Never gonna shower] [Never gonna give you up]
fn main() { let mut x = vec![4, 3, 2]; let y = x.clone(); x[0] = 99; println!("x is {:?}", x); println!("y is {:?}", y); }
x is [99, 3, 2] y is [4, 3, 2]
228. Copy a file
Copy the file at path src to dst.
复制文件
package main import ( "fmt" "io/ioutil" "log" "os" ) func main() { src, dst := "/tmp/file1", "/tmp/file2" err := copy(dst, src) if err != nil { log.Fatalln(err) } stat, err := os.Stat(dst) if err != nil { log.Fatalln(err) } fmt.Println(dst, "exists, it has size", stat.Size(), "and mode", stat.Mode()) } func copy(dst, src string) error { data, err := ioutil.ReadFile(src) if err != nil { return err } stat, err := os.Stat(src) if err != nil { return err } return ioutil.WriteFile(dst, data, stat.Mode()) } func init() { data := []byte("Hello") err := ioutil.WriteFile("/tmp/file1", data, 0644) if err != nil { log.Fatalln(err) } }
or
package main import ( "fmt" "io/ioutil" "log" "os" ) func main() { src, dst := "/tmp/file1", "/tmp/file2" err := copy(dst, src) if err != nil { log.Fatalln(err) } stat, err := os.Stat(dst) if err != nil { log.Fatalln(err) } fmt.Println(dst, "exists, it has size", stat.Size(), "and mode", stat.Mode()) } func copy(dst, src string) error { data, err := ioutil.ReadFile(src) if err != nil { return err } stat, err := os.Stat(src) if err != nil { return err } err = ioutil.WriteFile(dst, data, stat.Mode()) if err != nil { return err } return os.Chmod(dst, stat.Mode()) } func init() { data := []byte("Hello") err := ioutil.WriteFile("/tmp/file1", data, 0777) if err != nil { log.Fatalln(err) } err = os.Chmod("/tmp/file1", 0777) if err != nil { log.Fatalln(err) } }
or
package main import ( "fmt" "io" "io/ioutil" "log" "os" ) func main() { src, dst := "/tmp/file1", "/tmp/file2" err := copy(dst, src) if err != nil { log.Fatalln(err) } stat, err := os.Stat(dst) if err != nil { log.Fatalln(err) } fmt.Println(dst, "exists, it has size", stat.Size(), "and mode", stat.Mode()) } func copy(dst, src string) error { f, err := os.Open(src) if err != nil { return err } defer f.Close() stat, err := f.Stat() if err != nil { return err } g, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, stat.Mode()) if err != nil { return err } defer g.Close() _, err = io.Copy(g, f) if err != nil { return err } return os.Chmod(dst, stat.Mode()) } func init() { data := []byte("Hello") err := ioutil.WriteFile("/tmp/file1", data, 0777) if err != nil { log.Fatalln(err) } err = os.Chmod("/tmp/file1", 0777) if err != nil { log.Fatalln(err) } }
use std::fs; fn main() { let src = "/etc/fstabZ"; let dst = "fstab.bck"; let r = fs::copy(src, dst); match r { Ok(v) => println!("Copied {:?} bytes", v), Err(e) => println!("error copying {:?} to {:?}: {:?}", src, dst, e), } }
