使用pthread进行二进制搜索

二进制搜索是一种在排序数组或列表中搜索的流行方法。它只是将列表分为两半，并丢弃拥有密钥的可能性为零的一半。在划分时，我们检查键的中点，如果键小于中点，则使用下半部分；如果键大于中点，则使用上半部分。二进制搜索的时间复杂度为O(log(n))。

二进制搜索也可以使用多线程来实现，在这种情况下，我们通过为每个线程提供一部分列表来搜索关键字来利用处理器的内核。

线程数取决于处理器具有的内核数，最好为每个内核创建一个线程。

例子：

Input :  list = 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220
         key = 7
Output : 7 found in list

Input :  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

注–建议在基于Linux的系统中执行该程序。
使用以下代码在linux中编译：

g++ -pthread program_name.cpp

// CPP Program to perform binary search using pthreads
#include 
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;
}

输出：

110 found in array