Binary search only works efficiently on sorted containers. If your container is unsorted, you first need to sort it before performing a binary search.

Attempting a binary search on an unsorted container will lead to incorrect results because binary search relies on the order of elements to function correctly.

Here's a step-by-step approach to handle this:

First, use `std::sort()`

to sort your container. For example, if you have a `std::vector`

:

```
#include <algorithm>
#include <iostream>
#include <vector>
int main() {
std::vector<int> Numbers{3, 1, 4, 5, 2};
std::sort(Numbers.begin(), Numbers.end());
for (const auto& num : Numbers) {
std::cout << num << " ";
}
}
```

`1 2 3 4 5`

After sorting, you can perform a binary search using `std::binary_search()`

or `std::ranges::binary_search()`

:

```
#include <algorithm>
#include <iostream>
#include <vector>
int main() {
std::vector<int> Numbers{1, 2, 3, 4, 5};
bool found = std::binary_search(
Numbers.begin(), Numbers.end(), 4);
std::cout << "The number 4 "
<< (found ? "was" : "was not") << " found";
}
```

`The number 4 was found`

If you often need to search unsorted containers, consider using data structures like `std::set`

or `std::map`

, which maintain order internally. These containers are always sorted, making searches efficient without the need for explicit sorting.

Using `std::set`

:

```
#include <iostream>
#include <set>
int main() {
std::set<int> Numbers{3, 1, 4, 5, 2};
auto it = Numbers.find(4);
if (it != Numbers.end()) {
std::cout << "The number 4 was found";
} else {
std::cout << "The number 4 was not found";
}
}
```

`The number 4 was found`

Sorting your container before performing binary search ensures you get correct results and leverages the efficiency of binary search.

Answers to questions are automatically generated and may not have been reviewed.

This Question is from the Lesson:### Binary Search in C++

An introduction to the advantages of binary search, and how to use it with the C++ standard library algorithms `binary_search()`

, `lower_bound()`

, `upper_bound()`

, and `equal_range()`