Skip to main content

An attempt to Implement Binary Search STL (associative) Containers agnostic way.

 Binary Search is a very trivial algorithm to search a target value from a sorted array. It's popular among students of computer science and also during interviews it gets asked by the interviewer. It's easy. We take an array of integers already sorted and apply binary search on that array to figure out if the target value does present in that sorted array or not. 

The condition can be either present or not present. If it is present we return the array index of the element else we return -1.

The algorithm is very simple, it's broken down into three parts.

1. Find and compare the middle element of the search space with the key.

2. If the key is found in the middle, just return the array index.

3. If the key is not found then choose half of the array space, based on whether the key value is smaller or greater than the mid element. 

    a. If the key element is smaller than the mid element, then the left side of the search space will be used otherwise, the right side of the search space will be used. 

This process continues until the element is found in the search space or the total search space is exhausted. 

The very standard implementation is more or less like the below in C++:

int BinarySearch(const std::vector<int>& vec, const int&& target)
{
    if (vec.size() == 0) return -1;
    int left = 0;
    int right = static_cast<int>(vec.size() - 1);

    while (left <= right)
    {
        int mid = left + ((right - left) >> 2);
        if (vec[mid] == target) return mid;
        if (vec[mid] < target) left = mid + 1;
        else right = mid - 1;
    }
    return -1;
}

int main()
{
    std::vector<int> v = 
    { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 
       17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 
       31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 
       45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 
       59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 
       73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 
       87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100 };

    std::cout << "Non templated Imp(std::vector used): " << BinarySearch(v, 2) << "\n";
    std::cout << "Non templated Imp(std::vector used): " << BinarySearch(v, 99) << "\n";
    std::cout << "Non templated Imp(std::vector used): " << BinarySearch(v, 300) << "\n";

    return 0;
}

And it works. But now comes the twist, what if we want a binary search implementation that should work for most of the STLs associative containers like vector, list, array, and deque. In summary, want an implementation for STLs associative containers like vector, array, list, and deque. The idea is to develop the binary search in such a way that it can work container agnostic way. Hence followed templated approach and instead of passing the container itself used Iterator. It's a templatized Iterator-based approach. The below implementation works for std::vector, std::list, std::array, std::deque, and std::set. I've used visual studio 2022 for my implementation and the code looks like the below:

template<typename T, typename It>
_int64 BinarySearchT(It begin, It end, const T&& target)
{
    if (begin == end) 
        return -1;

    It left = begin;
    It right = std::prev(end);

    // Check for a container with one element
    if (left == right)
    {
        if (*left == target) return 0;
        else return -1;
    }

    while (left != end)
    {
        auto mid = left;
        std::advance(mid, std::distance(left, right) >> 2);
        if (*mid == target) return std::distance(begin, mid);
        else if (*mid < target) {
            left = mid;
            std::advance(left, 1);
        }
        else 
        {
            right = mid;
            end = right;
            std::advance(right, -1);
        }
    }

    return -1;
}

As we can see I have used Iterators to search the key element in search space(containers) which could be a std::array or std::vector or std::list or std::deque or std::set. 

Here is the complete demo code:

*For GCC compiler function return shall be int64_t instead of _int64. 
** The implementation doesn't work for std::forward_list.
Labels:

Comments

Post a Comment

Popular posts from this blog

Reversing char array without splitting the array to tokens

 I was reading about strdup, a C++ function and suddenly an idea came to my mind if this can be leveraged to aid in reversing a character array without splitting the array into words and reconstructing it again by placing spaces and removing trailing spaces. Again, I wanted an array to be passed as a function argument and an array size to be passed implicitly with the array to the function. Assumed, a well-formed char array has been passed into the function. No malformed array checking is done inside the function. So, the function signature and definition are like below: Below is the call from the client code to reverse the array without splitting tokens and reconstructing it. Finally, copy the reversed array to the destination.  For GNU C++, we should use strdup instead _strdup . On run, we get the following output: Demo code
Post a Comment
Read more

A simple approach to generate Fibonacci series via multi-threading

T his is a very simple approach taken to generate the Fibonacci series through multithreading. Here instead of a function, used a function object. The code is very simple and self-explanatory.  #include <iostream> #include <mutex> #include <thread> class Fib { public:     Fib() : _num0(1), _num1(1) {}     unsigned long operator()(); private:     unsigned long _num0, _num1;     std::mutex mu; }; unsigned long Fib::operator()() {     mu.lock(); // critical section, exclusive access to the below code by locking the mutex     unsigned long  temp = _num0;     _num0 = _num1;     _num1 = temp + _num0;     mu.unlock();     return temp; } int main() {     Fib f;          int i = 0;     unsigned long res = 0, res2= 0, res3 = 0;     std::cout << "Fibonacci series: ";     while (i <= 15) {         std::thread t1([&] { res = f(); }); // Capturing result to respective variable via lambda         std::thread t2([&] { res2 = f(); });         std::thread t3(
Post a Comment
Read more

Close a Window Application from another application.

 This is just a demo application code to show how the WM_CLOSE message can be sent to the target process which has a titled window to close the application. To achieve this, either we can use SendMessage or PostMessage APIs to send required Windows messages to the target application. Though both the APIs are dispatching WM_XXXXX message to target application two APIs has some differences, these are as below: 1. SendMessage () call is a blocking call but PostMessage is a non-blocking call(Asynchronous) 2. SendMessage() APIs return type is LRESULT (LONG_PTR) but PostMessage() APIs return type is BOOL(typedef int). In Short, SendMessage () APIs return type depends on what message has been sent to the Windowed target process. For the other one, it's always a non-zero value, which indicates the message has been successfully placed on the target process message queue. Now let's see how can I close a target windowed application "Solitaire & Casual Games" from my custom-
Post a Comment
Read more