std::binary_search
| Defined in header <algorithm>
|
||
template< class ForwardIt, class T >
bool binary_search( ForwardIt first, ForwardIt last, const T& value );
|
(1) | |
template< class ForwardIt, class T, class Compare >
bool binary_search( ForwardIt first, ForwardIt last, const T& value, Compare comp );
|
(2) | |
Checks if an element equivalent to value appears within the range [first, last), which must be partitioned with respect to the comparison against value. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.
Specifically, for std::binary_search to succeed, the range must satisfy all of the following requirements:
- partitioned with respect to
element < valueorcomp(element, value) - partitioned with respect to
!(value < elementor!comp(value, element) - for all elements, if
element < valueorcomp(element, value)istruethen!(value < element)or!comp(value, element)is alsotrue
Parameters
| first, last | - | the range of elements to examine | ||
| value | - | value to compare the elements to | ||
| comp | - | comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than the second.The signature of the comparison function should be equivalent to the following:
While the signature does not need to have
| ||
| Type requirements | ||||
Return value
true if an element equal to value is found, false otherwise.
Complexity
The number of comparisons performed is logarithmic in the distance between first and last
Possible implementation
| First version |
|---|
template<class ForwardIt, class T>
bool binary_search(ForwardIt first, ForwardIt last, const T& value)
{
first = std::lower_bound(first, last, value);
return (!(first == last) && !(value < *first));
}
|
| Second version |
template<class ForwardIt, class T, class Compare>
bool binary_search(ForwardIt first, ForwardIt last, const T& value, Compare comp)
{
first = std::lower_bound(first, last, value, comp);
return (!(first == last) && !(comp(value, *first));
}
|
Example
#include <iostream>
#include <algorithm>
#include <vector>
int main()
{
std::vector<int> haystack {1, 3, 4, 5, 9};
std::vector<int> needles {1, 2, 3};
for (auto needle : needles) {
std::cout << "Searching for " << needle << '\n';
if (std::binary_search(haystack.begin(), haystack.end(), needle)) {
std::cout << "Found " << needle << '\n';
} else {
std::cout << "no dice!\n";
}
}
}
Output:
Searching for 1
Found 1
Searching for 2
no dice!
Searching for 3
Found 3
See also
| returns range of elements matching a specific key (function template) |