Binary Search using pthread
Last Updated :
27 Dec, 2023
Binary search is a popular method of searching in a sorted array or list. It simply divides the list into two halves and discards the half which has zero probability of having the key. On dividing, we check the midpoint for the key and use the lower half if the key is less than the midpoint and the upper half if the key is greater than the midpoint. Binary search has a time complexity of O(log(n)). Binary search can also be implemented using multi-threading where we utilize the cores of the processor by providing each thread a portion of the list to search for the key. The number of threads depends upon the number of cores your processor has and it's better to create one thread for each core. Examples:
Input : list = 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220
key = 7
Output : 7 found in listInput : list = 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220
key = 111
Output : 111 not found in list
Note - It is advised to execute the program in Linux based system. Compile in Linux using the following code:
g++ -pthread program_name.cpp
CPP
// CPP Program to perform binary search using pthreads
#include <iostream>
using namespace std;
// size of array
#define MAX 16
// maximum number of threads
#define MAX_THREAD 4
// array to be searched
int a[] = { 1, 5, 7, 10, 12, 14, 15, 18,
20, 22, 25, 27, 30, 64, 110, 220 };
// key that needs to be searched
int key = 110;
bool found = false;
int part = 0;
void* binary_search(void* arg)
{
// Each thread checks 1/4 of the array for the key
int thread_part = part++;
int mid;
int low = thread_part * (MAX / 4);
int high = (thread_part + 1) * (MAX / 4);
// search for the key until low < high
// or key is found in any portion of array
while (low < high && !found) {
// normal iterative binary search algorithm
mid = (high - low) / 2 + low;
if (a[mid] == key) {
found = true;
break;
}
else if (a[mid] > key)
high = mid - 1;
else
low = mid + 1;
}
}
// Driver Code
int main()
{
pthread_t threads[MAX_THREAD];
for (int i = 0; i < MAX_THREAD; i++)
pthread_create(&threads[i], NULL, binary_search,
(void*)NULL);
for (int i = 0; i < MAX_THREAD; i++)
pthread_join(threads[i], NULL);
// key found in array
if (found)
cout << key << " found in array" << endl;
// key not found in array
else
cout << key << " not found in array" << endl;
return 0;
}
import java.util.concurrent.atomic.AtomicInteger;
public class Program {
// Size of array
static final int MAX = 16;
// Maximum number of threads
static final int MAX_THREAD = 4;
// Initial array
static int[] arr = { 1, 5, 7, 10, 12, 14, 15, 18,
20, 22, 25, 27, 30, 64, 110, 220 };
// Key that needs to be searched
static int key = 110;
static boolean found = false;
static AtomicInteger part = new AtomicInteger(0);
// Function to perform Binary Search
static void binarySearch()
{
int thread_part = part.getAndIncrement();
// Each thread checks 1/4 of the array for the key
int low = thread_part * (MAX / 4);
int high = (thread_part + 1) * (MAX / 4);
while (low < high && !found) {
// Normal iterative binary search algorithm
int mid = low + (high - low) / 2;
if (arr[mid] == key) {
found = true;
break;
}
else if (arr[mid] > key) {
high = mid - 1;
}
else {
low = mid + 1;
}
}
}
// Driver Code
public static void main(String[] args)
{
Thread[] thread = new Thread[MAX_THREAD];
for (int i = 0; i < MAX_THREAD; i++) {
thread[i]
= new Thread(new Runnable() {
public void run() {
binarySearch();
}
});
thread[i].start();
}
for (int i = 0; i < MAX_THREAD; i++) {
try {
thread[i].join();
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
if (found) {
System.out.printf("%d found in array\n", key);
}
else {
System.out.printf("%d not found in array\n",key);
}
}
}
// This code is contributed by shivhack999
# Python3 Program to find sum of array
# using multi-threading
from threading import Thread
# Size of array
MAX = 16
# Maximum number of threads
MAX_THREAD = 4
# Initial array
arr = [1, 5, 7, 10, 12, 14, 15, 18,
20, 22, 25, 27, 30, 64, 110, 220]
# Key that needs to be searched
key = 110
found = False
part = 0
# Function to perform Binary Search
def binary_search():
global part, found
thread_part = part
part += 1
# Each thread checks 1/4 of the array for the key
low = int(thread_part*(MAX/4))
high = int((thread_part+1)*(MAX/4))
# search for the key until low < high
# or key is found in any portion of array
while (low < high and not found):
# normal iterative binary search algorithm
mid = int(low + (high-low)/2)
if arr[mid] == key:
found = True
break
elif arr[mid] > key:
high = mid - 1
else:
low = mid + 1
# Driver Code
if __name__ == "__main__":
# Creating list of size MAX_THREAD
thread = list(range(MAX_THREAD))
# Creating MAX_THEAD number of threads
for i in range(MAX_THREAD):
thread[i] = Thread(target=binary_search)
thread[i].start()
# Waiting for all threads to finish
for i in range(MAX_THREAD):
thread[i].join()
# Key found in array
if found:
print("%d found in array" % key)
else:
print("%d not found in array" % key)
using System;
using System.Threading;
public class Program {
// Size of array
const int MAX = 16;
// Maximum number of threads
const int MAX_THREAD = 4;
// Initial array
static int[] arr = { 1, 5, 7, 10, 12, 14, 15, 18,
20, 22, 25, 27, 30, 64, 110, 220 };
// Key that needs to be searched
static int key = 110;
static bool found = false;
static int part = 0;
// Function to perform Binary Search
static void BinarySearch()
{
int thread_part
= Interlocked.Increment(ref part) - 1;
// Each thread checks 1/4 of the array for the key
int low = thread_part * (MAX / 4);
int high = (thread_part + 1) * (MAX / 4);
// Search for the key until low < high
// or key is found in any portion of array
while (low < high && !found) {
// Normal iterative binary search algorithm
int mid = low + (high - low) / 2;
if (arr[mid] == key) {
found = true;
break;
}
else if (arr[mid] > key) {
high = mid - 1;
}
else {
low = mid + 1;
}
}
}
// Driver Code
static void Main()
{
// Creating array of size MAX_THREAD
Thread[] thread = new Thread[MAX_THREAD];
// Creating MAX_THREAD number of threads
for (int i = 0; i < MAX_THREAD; i++) {
thread[i]
= new Thread(new ThreadStart(BinarySearch));
thread[i].Start();
}
// Waiting for all threads to finish
for (int i = 0; i < MAX_THREAD; i++) {
thread[i].Join();
}
// Key found in array
if (found) {
Console.WriteLine("{0} found in array", key);
}
else {
Console.WriteLine("{0} not found in array",
key);
}
}
}
// This code is contributed by shiv1o43g
// Size of array
const MAX = 16;
// Maximum number of threads
const MAX_THREAD = 4;
// Initial array
const arr = [1, 5, 7, 10, 12, 14, 15, 18,
20, 22, 25, 27, 30, 64, 110, 220];
// Key that needs to be searched
const key = 110;
let found = false;
let part = 0;
// Function to perform Binary Search
function binarySearch() {
const threadPart = part;
part += 1;
// Each thread checks 1/4 of the array for the key
let low = Math.floor(threadPart * (MAX / 4));
let high = Math.floor((threadPart + 1) * (MAX / 4));
// Search for the key until low < high
// or key is found in any portion of the array
while (low < high && !found) {
// Normal iterative binary search algorithm
const mid = Math.floor(low + (high - low) / 2);
if (arr[mid] === key) {
found = true;
break;
} else if (arr[mid] > key) {
high = mid - 1;
} else {
low = mid + 1;
}
}
}
// Driver Code
// Creating MAX_THREAD number of threads
const threads = new Array(MAX_THREAD).fill(null).map(() => {
return new Promise(resolve => {
binarySearch();
resolve();
});
});
// Waiting for all threads to finish
Promise.all(threads).then(() => {
// Key found in array
if (found) {
console.log(`${key} found in array`);
} else {
console.log(`${key} not found in array`);
}
});
Time complexity: O(log(n))
Space complexity: O(1)
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