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Binary Search in C++ Standard Template Library (STL)

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Binary search is a widely used searching algorithm that requires the array to be sorted before search is applied. The main idea behind this algorithm is to keep dividing the array in half (divide and conquer) until the element is found, or all the elements are exhausted.
It works by comparing the middle item of the array with our target, if it matches, it returns true otherwise if the middle term is greater than the target, the search is performed in the left sub-array. 
If the middle term is less than the target, the search is performed in the right sub-array.


The prototype for binary search is : 

binary_search(startaddress, 
              endaddress, valuetofind)
Parameters :
startaddress: the address of the first 
              element of the array.
endaddress: the address of the next contiguous 
            location of the last element of the array.
valuetofind: the target value which we have 
             to search for.
Returns :
true if an element equal to valuetofind is found, else false.

CPP

// CPP program to implement
// Binary Search in
// Standard Template Library (STL)
#include <algorithm>
#include <iostream>
  
using namespace std;
  
void show(int a[], int arraysize)
{
    for (int i = 0; i < arraysize; ++i)
        cout << a[i] << ",";
}
  
int main()
{
    int a[] = { 1, 5, 8, 9, 6, 7, 3, 4, 2, 0 };
    int asize = sizeof(a) / sizeof(a[0]);
    cout << "\nThe array is : \n";
    show(a, asize);
  
    cout << "\n\nLet's say we want to search for ";
    cout << "\n2 in the array So, we first sort the array";
    sort(a, a + asize);
    cout << "\n\nThe array after sorting is : \n";
    show(a, asize);
    cout << "\n\nNow, we do the binary search";
    if (binary_search(a, a + 10, 2))
        cout << "\nElement found in the array";
    else
        cout << "\nElement not found in the array";
  
    cout << "\n\nNow, say we want to search for 10";
    if (binary_search(a, a + 10, 10))
        cout << "\nElement found in the array";
    else
        cout << "\nElement not found in the array";
  
    return 0;
}

                    

Output
The array is : 
1,5,8,9,6,7,3,4,2,0,

Let's say we want to search for 
2 in the array So, we first sort the array

The array after sorting is : 
0,1,2,3,4,5,6,7,8,9,

Now, we do the binary search
Element found in the array

Now, say we want to search for 10
Element not found in the array

Time Complexity: sort – O(nlogn), binary_search – O(logn)
Auxiliary Space: O(1)

Related Article: std::bsearch in C++ 



Last Updated : 10 Jan, 2023
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