def quick_sort(arr):
    if len(arr) <= 1:
        return arr
    else:
        pivot = arr[0]
        left = [x for x in arr[1:] if x <= pivot]
        right = [x for x in arr[1:] if x > pivot]
        return quick_sort(left) + [pivot] + quick_sort(right)

# Example usage:
input_array = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]
sorted_array = quick_sort(input_array)

print("Original Array:", input_array)
print("Sorted Array:", sorted_array)

<?php

function quickSort(array $array): array
{
    $length = count($array);

    if ($length <= 1) {
        return $array;
    }

    $pivot = $array[0];
    $left = $right = [];

    for ($i = 1; $i < $length; $i++) {
        if ($array[$i] < $pivot) {
            $left[] = $array[$i];
        } else {
            $right[] = $array[$i];
        }
    }

    return array_merge(quickSort($left), [$pivot], quickSort($right));
}

// Example usage:
$array = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5];
$sortedArray = quickSort($array);

echo "Original Array: " . implode(", ", $array) . "\n";
echo "Sorted Array: " . implode(", ", $sortedArray) . "\n";

package main

import (
	"errors"
	"fmt"
	"os"
)

func main() {
	filePath := "file.txt"

	if _, err := os.Stat(filePath); errors.Is(err, os.ErrNotExist) {
		fmt.Println("file not exists")
	} else {
		fmt.Println("file exists")
	}
}

package main

import (
	"fmt"
	"time"
)

func main() {
	firstTimer := time.NewTimer(3 * time.Second)
	value := <-firstTimer.C // value is a current time

	fmt.Printf("first timer expired: %v\n", value) // the line printed 3 seconds after running code

	secondTimer := time.NewTimer(2 * time.Second)

	go func() {
		<-secondTimer.C
		fmt.Println("second timer expired") // the line is not printed because the second timer is stopped before expiration
	}()

	stop := secondTimer.Stop() // stop second timer before it expired

	if stop {
		fmt.Println("second timer is stopped")
	}
}

// $ go run timers.go
// first timer expired: 2024-02-09 22:32:57.570649221 +0700 +07 m=+3.002054417
// second timer is stopped

package main

import (
	"fmt"
	"sync"
	"sync/atomic"
)

func main() {
	var atomicCounter, nonAtomicCounter uint64
	wg := sync.WaitGroup{}

	for i := 0; i < 50; i++ {
		wg.Add(1)

		go func() { // run 50 goroutines, each goroutine increases the counter 1000 times
			for c := 0; c < 1000; c++ {
				atomic.AddUint64(&atomicCounter, 1) // increase atomic counter
				nonAtomicCounter++ // increase non-atomic counter
			}

			wg.Done()
		}()
	}

	wg.Wait() // wait until all goroutines finish
	
	fmt.Println("atomic counter value:", atomicCounter)
	fmt.Println("non atomic counter value:", nonAtomicCounter)
}

// go run counters.go 
// atomic counter value: 50000
// non atomic counter value: 30648

package main

import "fmt"

func main() {
    // Recover function must be called inside a deferred function.
    // When the enclosing function panics, defer is activated and the restore call inside it catches the panic.
    defer func() {
        if r := recover(); r != nil {
            fmt.Printf("recovered: %s\n", r)
        }
    }()

    panic("some fatal error")
    
    // This code won't run because of panic.
    // Basic operations stop during a panic and resume during a deferred close.
    fmt.Println("after panic")
}

import csv

# Writing to a CSV file
with open('data.csv', 'w', newline='') as csvfile:
    fieldnames = ['name', 'age', 'city']
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

    writer.writeheader()
    writer.writerow({'name': 'John', 'age': 30, 'city': 'New York'})
    writer.writerow({'name': 'Alice', 'age': 25, 'city': 'London'})

# Reading from a CSV file
with open('data.csv', newline='') as csvfile:
    reader = csv.DictReader(csvfile)
    for row in reader:
        print(row)

package main

import (
    "fmt"
    "time"
)

func main() {
    // in this example we will choose between two channels
    c1 := make(chan string)
    c2 := make(chan string)

    go func() {
        time.Sleep(1 * time.Second)
        c1 <- "one"
    }()

    // each channel will receive a value after some time
    go func() {
        time.Sleep(2 * time.Second)
        c2 <- "two"
    }()

    // use select statement to wait for both values ​​at the same time,
    // printing each one as it arrives
    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.Println("received", msg1)
        case msg2 := <-c2:
            fmt.Println("received", msg2)
        }
    }
}

# Returns index of target in arr if present, else -1
def binary_search(arr, target):
	low = 0
	high = len(arr) - 1

	while low <= high:
		# Check base case
		mid = (high + low) // 2

		# If element is smaller than mid, then it can only
		# be present in left subarray
		if arr[mid] > target:
			high = mid - 1
		# Else the element can only be present in right subarray
		elif arr[mid] < target:
			low = mid + 1
		# If element is present at the middle itself
		else:
			return mid

	# Element is not present in the array
	return -1

# Test array
arr = [ 2, 3, 4, 10, 40 ]
target = 10

result = binary_search(arr, target)

if result != -1:
	print("Element is present at index", str(result))
else:
	print("Element is not present in array")

package main

import "fmt"

// return target index if it exists in arr
func search(arr []int, target int) int {
    low := 0
    high := len(arr) - 1

    for low <= high {
        mid := (low + high) / 2

        if arr[mid] < target {
            low = mid + 1
        } else if arr[mid] > target {
            high = mid - 1
        } else {
            return mid
        }
    }

    return -1
}

func main() {
    target := 7
    items := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
    fmt.Printf("Element '%d' index is %d", target, search(items, target))
}

// $ output
// 6

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	wg := &sync.WaitGroup{} // WaitGroup is used to wait for the execution of all running goroutines

	for i := 1; i <= 5; i++ {
		wg.Add(1) // launch several goroutines and increment the counter in WaitGroup for each running goroutine

		go func(id int) {
			worker(id, wg)
		}(i)
	}

	fmt.Println("waiting for all goroutines to complete")
	wg.Wait() // block the execution of the program until the WaitGroup counter becomes equal to 0 again
	fmt.Println("done")
}

func worker(id int, wg *sync.WaitGroup) {
	fmt.Printf("worker %d started\n", id)
	time.Sleep(time.Second) // Sleep simulates a long task
	
    fmt.Printf("worker %d finished\n", id)
	wg.Done() // notify WaitGroup that the worker has completed
}

// $ go run waitgroups.go 
// waiting for all goroutines finished
// worker 4 started
// worker 1 started
// worker 2 started
// worker 3 started
// worker 2 finished
// worker 4 finished
// worker 1 finished
// worker 3 finished
// done

package main

import (
    "fmt"
    "net/http"
)

func hello(w http.ResponseWriter, req *http.Request) {
    fmt.Fprintf(w, "Hello, World!\n")
}

func headers(w http.ResponseWriter, req *http.Request) {
    for name, headers := range req.Header {
        for _, h := range headers {
            fmt.Fprintf(w, "%v: %v\n", name, h)
        }
    }
}

func main() {
    http.HandleFunc("/hello", hello)
    http.HandleFunc("/headers", headers)

    http.ListenAndServe(":8080", nil) // run http server on port 8080
}

package main

import (
	"fmt"
	"time"
)

func main() {
	first := make(chan string, 1)

	go func() {
		time.Sleep(2 * time.Second) // wait 2 seconds before send value to channel
		first <- "first result"     // send value to the channel
	}()

	select {
	case result := <-first:
		fmt.Println(result)
	case <-time.After(time.Second): // timeout occurs before the value is read from the first channel
		fmt.Println("first timeout")
	}

	second := make(chan string, 1)

	go func() {
		time.Sleep(time.Second)   // wait 1 second before send value to the channel
		second <- "second result" // send value to the channel
	}()

	select {
	case result := <-second: // the value from the channel is read before the timeout expires
		fmt.Println(result)
	case <-time.After(2 * time.Second):
		fmt.Println("second timeout")
	}
}

// $ go run timeouts.go 
// first timeout
// second result

package main

import (
	"fmt"
	"time"
)

func main() {
	ticker := time.NewTicker(time.Second)
	fmt.Println("ticker is started")

	done := make(chan struct{})

	go func() {
		for {
			select {
			case <-done:
				return
			case t := <-ticker.C:
				fmt.Println("tick", t)
			}
		}
	}()

	time.Sleep(5 * time.Second)

	ticker.Stop()
	fmt.Println("ticker is stopped")

	time.Sleep(5 * time.Second)
	done <- struct{}{}
}

// go run tickers.go 
// ticker is started
// tick 2024-02-09 23:40:25.809616086 +0700 +07 m=+1.000091237
// tick 2024-02-09 23:40:26.809742343 +0700 +07 m=+2.000152938
// tick 2024-02-09 23:40:27.809804037 +0700 +07 m=+3.000214622
// tick 2024-02-09 23:40:28.809852444 +0700 +07 m=+4.000263029
// ticker is stopped
// tick 2024-02-09 23:40:29.809908932 +0700 +07 m=+5.000319557

<?php 
  
function binarySearch(array $arr, int $target): int 
{ 
    $low = 0; 
    $high = count($arr) - 1; 
      
    while ($low <= $high) {          
        // compute middle index 
        $mid = floor(($low + $high) / 2);  
  
        if ($arr[$mid] > $target) { 
            // search the left side of the array 
            $high = $mid -1; 
        } else if ($arr[$mid] < $target) { 
            // search the right side of the array 
            $low = $mid + 1; 
        } else {
            // element found at mid 
            return $mid; 
        }
    } 
      
    // If we reach here element x doesnt exist 
    return -1; 
} 
  
// Driver code 
$arr = [1, 2, 3, 4, 5]; 
$target = 3;
$result = binarySearch($arr, $target);

if($result !== -1) { 
    echo "Target '$target' exists at position $result"; 
} else {
    echo "Target '$target' does not exist";
}

package main

import (
    "fmt"
    "time"
)

// the channel is used to notify main goroutine that the function completed successfully
func worker(done chan bool) {
    fmt.Println("working...")
    time.Sleep(time.Second)
    fmt.Println("done")

    done <- true // send a value to indicate that the function completed successfully
}

func main() {
    done := make(chan bool, 1) // create a buffered channel for notification
    go worker(done) // run worker

    <-done // blocked until a notification is received from the worker from the channel
           // if you remove the line <- done the program will close before the worker starts
}

package main

import (
    "fmt"
    "time"
)

// this is a worker that we will run in several parallel instances
// these workers will receive tasks through the 'jobs' channel and send the results to 'results'
// we will wait for one second for each task to simulate heavy requests
func worker(id int, jobs <-chan int, results chan<- int) {
    for j := range jobs {
        fmt.Println("worker", id, "started job", j)
        time.Sleep(time.Second)
        fmt.Println("worker", id, "finished job", j)
        results <- j * 2
    }
}

func main() {
    // to use worker pool, we need to send a task and receive the execution results
    // therefore 2 channels are created
    jobs := make(chan int, 100)
    results := make(chan int, 100)

    // start 3 workers, initially blocked because no assignments yet
    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }

    // send 5 jobs and then close the channel, notofying that all jobs have been sent
    for j := 1; j <= 5; j++ {
        jobs <- j
    }

    close(jobs)

    // collect all the results
    // this also ensures that the goroutines have ended
    for a := 1; a <= 5; a++ {
        <-results
    }
}

package main

import (
    "fmt"
    "os"
    "os/signal"
    "syscall"
)

func main() {
    sigs := make(chan os.Signal, 1) // create channel for signal, it should be buffered
    signal.Notify(sigs, syscall.SIGINT) // register the channel to receive notifications of the specified signals
    done := make(chan bool, 1)

    go func() {
        sig := <-sigs // wait for OS signal, once received, notify main go routine
        fmt.Printf("\nos signal: %v\n", sig)
        done <- true
    }()

    fmt.Println("awaiting signal")
    <-done // wait for the expected signal and then exit
    fmt.Println("exiting")
}

// $ go run main.go 
// awaiting os signal
// ^C
// os signal: interrupt
// exiting program

package main

import (
	"fmt"
	"sync"
)

// without using mutex the following error can happen: "fatal error: concurrent map writes" while changing the map in multiple goroutines
type Storage struct {
	sync.Mutex
	storage map[string]int // map is not threade-safe
}

func (s *Storage) Increment(name string) {
	s.Lock() // lock the mutex before accessing counters
	defer s.Unlock() // unlock the mutex at the end of the function using a defer statement
    s.storage[name]++
}

func (s *Storage) Decrement(name string) {
	s.Lock()
    defer s.Unlock()
	s.storage[name]--
}

func main() {
	s := &Storage{
		storage: make(map[string]int),
	}

	wg := sync.WaitGroup{}
	wg.Add(5)

    // increment a named counter in a loop
	increment := func(name string, count uint) {
		for i := 0; i < int(count); i++ {
			s.Increment(name)
		}

		wg.Done()
	}

    // decrement a named counter in a loop
	decrement := func(name string, count uint) {
		for i := 0; i < int(count); i++ {
			s.Decrement(name)
		}

		wg.Done()
	}

    // run 5 goroutines concurrently
	go increment("a", 1000)
	go decrement("a", 500)

	go increment("b", 1000)
	go increment("b", 1000)
	go decrement("b", 1500)

	wg.Wait() // wait for the goroutines to finish

	fmt.Println(s.storage)
}

// $ go run main.go  
// map[a:500 b:500]

// without mutex the following error can happen
// $ go run main.go
// fatal error: concurrent map writes

package main

import (
	"bufio"
	"fmt"
	"net"
	"time"
)

type Client struct {
	conn net.Conn
}

func (c *Client) Write(content string) error {
	_, err := c.conn.Write([]byte(content + "\n"))

	return err
}

func (c *Client) Read() (string, error) {
	reader := bufio.NewReader(c.conn)

	return reader.ReadString('\n')
}

func (c *Client) Close() error {
	return c.conn.Close()
}

// create tcp client
func getClient(address string) (*Client, error) {
	// try to resolve address
	_, err := net.ResolveTCPAddr("tcp", address)

	if err != nil {
		return nil, err
	}

	// create tcp connection with 5s timeout 
	conn, err := net.DialTimeout("tcp", address, 5*time.Second)

	if err != nil {
		return nil, err
	}

	conn.SetReadDeadline(time.Now().Add(5 * time.Second))
	conn.SetWriteDeadline(time.Now().Add(5 * time.Second))

	return &Client{conn: conn}, nil
}

func main() {
	// see https://tcpbin.com/
	client, err := getClient("tcpbin.com:4242")

	if err != nil {
		panic(err)
	}

	// close the connection at the end
	defer client.Close()

	// send request to tcpbin.com echo server
	err = client.Write("Hello, World!!!")

	if err != nil {
		panic(err)
	}

	// read response from tcpbin.com echo server
	content, err := client.Read()

	if err != nil {
		panic(err)
	}

	fmt.Print(content)
}

// $ go run main.go 
// Hello, World!!!