题图来自 Go vs. Rust performance comparison: The basics
61. Get current date
获取当前时间
package main
import (
"fmt"
"time"
)
func main() {
d := time.Now()
fmt.Println("Now is", d)
// The Playground has a special sandbox, so you may get a Time value fixed in the past.
}
Now is 2009-11-10 23:00:00 +0000 UTC m=+0.000000001
extern crate time;
let d = time::now();
or
use std::time::SystemTime;
fn main() {
let d = SystemTime::now();
println!("{:?}", d);
}
SystemTime { tv_sec: 1526318418, tv_nsec: 699329521 }
62. Find substring position
字符串查找
查找子字符串位置
package main
import (
"fmt"
"strings"
)
func main() {
x := "été chaud"
{
y := "chaud"
i := strings.Index(x, y)
fmt.Println(i)
}
{
y := "froid"
i := strings.Index(x, y)
fmt.Println(i)
}
}
i is the byte index of y in x, not the character (rune) index. i will be -1 if y is not found in x.
6
-1
fn main() {
let x = "été chaud";
let y = "chaud";
let i = x.find(y);
println!("{:?}", i);
let y = "froid";
let i = x.find(y);
println!("{:?}", i);
}
Some(6)
None
63. Replace fragment of a string
替换字符串片段
package main
import (
"fmt"
"strings"
)
func main() {
x := "oink oink oink"
y := "oink"
z := "moo"
x2 := strings.Replace(x, y, z, -1)
fmt.Println(x2)
}
moo moo moo
fn main() {
let x = "lorem ipsum dolor lorem ipsum";
let y = "lorem";
let z = "LOREM";
let x2 = x.replace(&y, &z);
println!("{}", x2);
}
LOREM ipsum dolor LOREM ipsum
64. Big integer : value 3 power 247
超大整数
package main
import "fmt"
import "math/big"
func main() {
x := new(big.Int)
x.Exp(big.NewInt(3), big.NewInt(247), nil)
fmt.Println(x)
}
7062361041362837614435796717454722507454089864783271756927542774477268334591598635421519542453366332460075473278915787
extern crate num;
use num::bigint::ToBigInt;
fn main() {
let a = 3.to_bigint().unwrap();
let x = num::pow(a, 247);
println!("{}", x)
}
7062361041362837614435796717454722507454089864783271756927542774477268334591598635421519542453366332460075473278915787
65. Format decimal number
格式化十进制数
package main
import "fmt"
func main() {
x := 0.15625
s := fmt.Sprintf("%.1f%%", 100.0*x)
fmt.Println(s)
}
15.6%
fn main() {
let x = 0.15625f64;
let s = format!("{:.1}%", 100.0 * x);
println!("{}", s);
}
15.6%
66. Big integer exponentiation
大整数幂运算
package main
import "fmt"
import "math/big"
func exp(x *big.Int, n int) *big.Int {
nb := big.NewInt(int64(n))
var z big.Int
z.Exp(x, nb, nil)
return &z
}
func main() {
x := big.NewInt(3)
n := 5
z := exp(x, n)
fmt.Println(z)
}
243
extern crate num;
use num::bigint::BigInt;
fn main() {
let x = BigInt::parse_bytes(b"600000000000", 10).unwrap();
let n = 42%
67. Binomial coefficient "n choose k"
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.
二项式系数“n选择k”
package main
import (
"fmt"
"math/big"
)
func main() {
z := new(big.Int)
z.Binomial(4, 2)
fmt.Println(z)
z.Binomial(133, 71)
fmt.Println(z)
}
6
555687036928510235891585199545206017600
extern crate num;
use num::bigint::BigInt;
use num::bigint::ToBigInt;
use num::traits::One;
fn binom(n: u64, k: u64) -> BigInt {
let mut res = BigInt::one();
for i in 0..k {
res = (res * (n - i).to_bigint().unwrap()) /
(i + 1).to_bigint().unwrap();
}
res
}
fn main() {
let n = 133;
let k = 71;
println!("{}", binom(n, k));
}
555687036928510235891585199545206017600
68. Create a bitset
创建位集合
package main
import (
"fmt"
"math/big"
)
func main() {
var x *big.Int = new(big.Int)
x.SetBit(x, 42, 1)
for _, y := range []int{13, 42} {
fmt.Println("x has bit", y, "set to", x.Bit(y))
}
}
x has bit 13 set to 0
x has bit 42 set to 1
or
package main
import (
"fmt"
)
const n = 1024
func main() {
x := make([]bool, n)
x[42] = true
for _, y := range []int{13, 42} {
fmt.Println("x has bit", y, "set to", x[y])
}
}
x has bit 13 set to false
x has bit 42 set to true
or
package main
import (
"fmt"
)
func main() {
const n = 1024
x := NewBitset(n)
x.SetBit(13)
x.SetBit(42)
x.ClearBit(13)
for _, y := range []int{13, 42} {
fmt.Println("x has bit", y, "set to", x.GetBit(y))
}
}
type Bitset []uint64
func NewBitset(n int) Bitset {
return make(Bitset, (n+63)/64)
}
func (b Bitset) GetBit(index int) bool {
pos := index / 64
j := index % 64
return (b[pos] & (uint64(1) << j)) != 0
}
func (b Bitset) SetBit(index int) {
pos := index / 64
j := index % 64
b[pos] |= (uint64(1) << j)
}
func (b Bitset) ClearBit(index int) {
pos := index / 64
j := index % 64
b[pos] ^= (uint64(1) << j)
}
x has bit 13 set to false
x has bit 42 set to true
fn main() {
let n = 20;
let mut x = vec![false; n];
x[3] = true;
println!("{:?}", x);
}
[false, false, false, true, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false]
69. Seed random generator
Use seed s to initialize a random generator.
If s is constant, the generator output will be the same each time the program runs. If s is based on the current value of the system clock, the generator output will be different each time.
随机种子生成器
package main
import (
"fmt"
"math/rand"
)
func main() {
var s int64 = 42
rand.Seed(s)
fmt.Println(rand.Int())
}
3440579354231278675
or
package main
import (
"fmt"
"math/rand"
)
func main() {
var s int64 = 42
r := rand.New(rand.NewSource(s))
fmt.Println(r.Int())
}
3440579354231278675
use rand::{Rng, SeedableRng, rngs::StdRng};
fn main() {
let s = 32;
let mut rng = StdRng::seed_from_u64(s);
println!("{:?}", rng.gen::<f32>());
}
0.35038823
70. Use clock as random generator seed
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run.
使用时钟作为随机生成器的种子
package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
rand.Seed(time.Now().UnixNano())
// Well, the playground date is actually fixed in the past, and the
// output is cached.
// But if you run this on your workstation, the output will vary.
fmt.Println(rand.Intn(999))
}
524
or
package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
r := rand.New(rand.NewSource(time.Now().UnixNano()))
// Well, the playground date is actually fixed in the past, and the
// output is cached.
// But if you run this on your workstation, the output will vary.
fmt.Println(r.Intn(999))
}
524
use rand::{Rng, SeedableRng, rngs::StdRng};
use std::time::SystemTime;
fn main() {
let d = SystemTime::now()
.duration_since(SystemTime::UNIX_EPOCH)
.expect("Duration since UNIX_EPOCH failed");
let mut rng = StdRng::seed_from_u64(d.as_secs());
println!("{:?}", rng.gen::<f32>());
}
0.7326781
71. Echo program implementation
Basic implementation of the Echo program: Print all arguments except the program name, separated by space, followed by newline.
The idiom demonstrates how to skip the first argument if necessary, concatenate arguments as strings, append newline and print it to stdout.
实现 Echo 程序
package main
import "fmt"
import "os"
import "strings"
func main() {
fmt.Println(strings.Join(os.Args[1:], " "))
}
use std::env;
fn main() {
println!("{}", env::args().skip(1).collect::<Vec<_>>().join(" "));
}
or
use itertools::Itertools;
println!("{}", std::env::args().skip(1).format(" "));
74. Compute GCD
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers.
计算大整数a和b的最大公约数x。使用能够处理大数的整数类型。
package main
import "fmt"
import "math/big"
func main() {
a, b, x := new(big.Int), new(big.Int), new(big.Int)
a.SetString("6000000000000", 10)
b.SetString("9000000000000", 10)
x.GCD(nil, nil, a, b)
fmt.Println(x)
}
3000000000000
extern crate num;
use num::Integer;
use num::bigint::BigInt;
fn main() {
let a = BigInt::parse_bytes(b"6000000000000", 10).unwrap();
let b = BigInt::parse_bytes(b"9000000000000", 10).unwrap();
let x = a.gcd(&b);
println!("{}", x);
}
3000000000000
75. Compute LCM
计算大整数a和b的最小公倍数x。使用能够处理大数的整数类型。
Compute the least common multiple x of big integers a and b. Use an integer type able to handle huge numbers.
package main
import "fmt"
import "math/big"
func main() {
a, b, gcd, x := new(big.Int), new(big.Int), new(big.Int), new(big.Int)
a.SetString("6000000000000", 10)
b.SetString("9000000000000", 10)
gcd.GCD(nil, nil, a, b)
x.Div(a, gcd).Mul(x, b)
fmt.Println(x)
}
18000000000000
extern crate num;
use num::bigint::BigInt;
use num::Integer;
fn main() {
let a = BigInt::parse_bytes(b"6000000000000", 10).unwrap();
let b = BigInt::parse_bytes(b"9000000000000", 10).unwrap();
let x = a.lcm(&b);
println!("x = {}", x);
}
x = 18000000000000
76. Binary digits from an integer
Create the string s of integer x written in base 2.
E.g. 13 -> "1101"
将十进制整数转换为二进制数字
package main
import "fmt"
import "strconv"
func main() {
x := int64(13)
s := strconv.FormatInt(x, 2)
fmt.Println(s)
}
1101
or
package main
import (
"fmt"
"math/big"
)
func main() {
x := big.NewInt(13)
s := fmt.Sprintf("%b", x)
fmt.Println(s)
}
1101
fn main() {
let x = 13;
let s = format!("{:b}", x);
println!("{}", s);
}
1101
77. SComplex number
Declare a complex x and initialize it with value (3i - 2). Then multiply it by i.
复数
package main
import (
"fmt"
"reflect"
)
func main() {
x := 3i - 2
x *= 1i
fmt.Println(x)
fmt.Print(reflect.TypeOf(x))
}
(-3-2i)
complex128
extern crate num;
use num::Complex;
fn main() {
let mut x = Complex::new(-2, 3);
x *= Complex::i();
println!("{}", x);
}
-3-2i
78. "do while" loop
Execute a block once, then execute it again as long as boolean condition c is true.
循环执行
package main
import (
"fmt"
"math/rand"
)
func main() {
for {
x := rollDice()
fmt.Println("Got", x)
if x == 3 {
break
}
}
}
func rollDice() int {
return 1 + rand.Intn(6)
}
Go has no do while loop, use the for loop, instead.
Got 6
Got 4
Got 6
Got 6
Got 2
Got 1
Got 2
Got 3
or
package main
import (
"fmt"
"math/rand"
)
func main() {
for done := false; !done; {
x := rollDice()
fmt.Println("Got", x)
done = x == 3
}
}
func rollDice() int {
return 1 + rand.Intn(6)
}
Got 6
Got 4
Got 6
Got 6
Got 2
Got 1
Got 2
Got 3
loop {
doStuff();
if !c { break; }
}
Rust has no do-while loop with syntax sugar. Use loop and break.
79. Convert integer to floating point number
Declare floating point number y and initialize it with the value of integer x .
整型转浮点型
声明浮点数y并用整数x的值初始化它。
package main
import (
"fmt"
"reflect"
)
func main() {
x := 5
y := float64(x)
fmt.Println(y)
fmt.Printf("%.2f\n", y)
fmt.Println(reflect.TypeOf(y))
}
5
5.00
float64
fn main() {
let i = 5;
let f = i as f64;
println!("int {:?}, float {:?}", i, f);
}
int 5, float 5.0
80. Truncate floating point number to integer
Declare integer y and initialize it with the value of floating point number x . Ignore non-integer digits of x . Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser).
浮点型转整型
package main
import "fmt"
func main() {
a := -6.4
b := 6.4
c := 6.6
fmt.Println(int(a))
fmt.Println(int(b))
fmt.Println(int(c))
}
-6
6
6
fn main() {
let x = 41.59999999f64;
let y = x as i32;
println!("{}", y);
}
41
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的Matlab代码详细注释及难点解释)
