C++, search, exponential_search.cpp

``````/**
* \file
* \brief [Exponential search
* algorithm](https://en.wikipedia.org/wiki/Exponential_search)
*
* The algorithm try to search the range where the key should be.
* If it has been found we do a binary search there.
* The range of the search grows by exponential every time.
* If the key is larger than the last element of array, the start of
* block(block_front) will be equal to the end of block(block_size) and the
* algorithm return null ponter, every other cases the algoritm return fom the
* loop.
*/
#include <cassert>
#include <cmath>
#include <iostream>
#ifdef _MSC_VER
#include <string>  // use for MS Visual C++
#else
#include <cstring>  // for all other compilers
#endif

/** Binary Search Algorithm (used by ::struzik_search)\n
* * Time Complexity O(log n) where 'n' is the number of elements
* * Worst Time Complexity O(log n)
* * Best Time Complexity Ω(1)
* * Space Complexity O(1)
* * Auxiliary Space Complexity O(1)
* \returns pointer to value in the array
*/
template <class Type>
inline Type* binary_s(Type* array, size_t size, Type key) {
int32_t lower_index(0), upper_index(size - 1), middle_index;

while (lower_index <= upper_index) {
middle_index = std::floor((lower_index + upper_index) / 2);

if (*(array + middle_index) < key)
lower_index = (middle_index + 1);
else if (*(array + middle_index) > key)
upper_index = (middle_index - 1);
else
return (array + middle_index);
}

return nullptr;
}

/** Struzik Search Algorithm(Exponential)
* * Time Complexity O(log i) where i is the position of search key in the list
* * Worst Time Complexity O(log i)
* * Best Time Complexity Ω(1)
* * Space Complexity O(1)
* * Auxiliary Space Complexity O(1)
*/
template <class Type>
Type* struzik_search(Type* array, size_t size, Type key) {
uint32_t block_front(0), block_size = size == 0 ? 0 : 1;
while (block_front != block_size) {
if (*(array + block_size - 1) < key) {
block_front = block_size;
(block_size * 2 - 1 < size) ? (block_size *= 2) : block_size = size;
continue;
}
return binary_s<Type>(array + block_front, (block_size - block_front),
key);
}
return nullptr;
}

/** Main function */
int main() {
// TEST CASES
int* sorted_array = new int[7]{7, 10, 15, 23, 70, 105, 203};
assert(struzik_search<int>(sorted_array, 7, 0) == nullptr);
assert(struzik_search<int>(sorted_array, 7, 1000) == nullptr);
assert(struzik_search<int>(sorted_array, 7, 50) == nullptr);
assert(struzik_search<int>(sorted_array, 7, 7) == sorted_array);
// TEST CASES
delete[] sorted_array;
return 0;
}
``````