std::binary_search() in C++ STL

In C++, STL provide std::binary_search() function which implements binary search algorithm to check whether an element exists in the given sorted range. It is defined inside <algorithm> header file. In this article, we will learn about std::binary_search() function in C++.

Example:

// C++ Program to illustrate the use of
// std::binary_search() method
#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v = {1, 3, 6, 8, 9};
    int k = 8;

    if (binary_search(v.begin(), v.end(), k))
        cout << k << " is Present";
    else
        cout << k << " is NOT Present";

    return 0;
}

8 is Present

binary_search() Syntax

std::binary_search(first, last, k, comp);

Parameters

• first: Iterator to the first element of the range.
• last: Iterator to the theoretical element just after the last element of range.
• k: The value to be search.
• comp: Custom comparator. By default, it returns true if k is equal to the current element in the range.

Return Value

• Returns true, if k is present in the given range.
• Returns false, if k is not present in the given range.

Note: Behaviour of binary_search() is undefined if the given range is not sorted as binary search algorithm can only be implemented on sorted data.

More Examples of binary_search()

The following examples demonstrates the different use cases of std::binary_seach() function:

Example 1: Checking if an Element Exists in Array using std::binary_search()

// C++ Program to check if an element exists in
// in an array using std::binary_search()
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {1, 4, 5, 7, 9};
    int n = sizeof(arr) / sizeof(arr[0]);
    int k = 7;

    // Check if the element exists
    if (binary_search(arr, arr + n, k))
        cout << k << " is Present";
    else
        cout << k << " is NOT Present";
    return 0;
}

78 is Present

Example 2: Using binary_search() on a Set Container

// C++ Program to check if an element exists in
// in an set using std::binary_search()
#include <bits/stdc++.h>
using namespace std;

int main() {
    set<int> s = {1, 4, 5, 7, 9};
    int k = 8;

    // Check if the element exists
    if (binary_search(s.begin(), s.end(), k))
        cout << k << " is Present";
    else
        cout << k << " is NOT Present";
    return 0;
}

11 is Present

Explanation: Even though set container does not have random access, binary_search() function still works because of the reason discussed below.

binary_search() in C++ STL

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