## C++, search, fibonacci_search.cpp

``````/**
* @author sprintyaf
* @file fibonacci_search.cpp
* @brief [Fibonacci search
* algorithm](https://en.wikipedia.org/wiki/Fibonacci_search_technique)
*/

#include <iostream>
#include <vector> // for std::vector class
#include <cassert> // for assert
#include <cstdlib> // for random numbers
#include <algorithm> // for sorting

/**
* @brief using fibonacci search algorithm finds an index of a given element in a sorted array
*
* @param arr sorted array
* @param value value that we're looking for
* @returns if the array contains the value, returns an index of the element. otherwise -1.
*/
int fibonacci_search(const std::vector<int> &arr, int value){
// initialize last and current members of Fibonacci sequence
int last = 0, current = 1;
int length = arr.size(); // array size
// next member of Fibonacci sequence which is "last" + "current"
int next = last + current;

// "next" will store the smallest Fibonacci number greater or equal to "length"
while(next < length){
last = current;
current = next;
next = last + current;
}

// "offset" is the end of eliminated range from front
int offset = -1, index;
// while loop until there are elements left to consider.
// when "next" becomes 1, last is equal to 0, so search is done,
// because arr[offset] will already be eliminated
while(next > 1){
// check if "last" is valid location
index = std::min(offset + last, length-1);
// if value is greater than the value at "index", eliminate the subarray from offset to index
if(arr[index] < value){
next = current;
current = last;
last = next - current;
offset = index;
// if value is less than the value at "index", eliminate the subarray after index+1
} else if(arr[index] > value){
next = last;
current = current - last;
last = next - current;
// element is found
} else {
return index;
}
}
// comparing the last element
if(current && !arr.empty() && arr[offset+1] == value){
return offset+1;
}
return -1;
}

/**
* @brief random tests for checking performance when an array doesn't contain an element
*/
bool no_occurence_tests(){
bool passed = true;
int rand_num, rand_value, index, num_tests = 1000;
std::vector<int> arr;
while(num_tests--){
arr.clear();
for(int i = 0; i < 100; i++){
rand_num = std::rand() % 1000;
arr.push_back(rand_num);
}
rand_value = std::rand() % 1000;
while(std::find(arr.begin(), arr.end(), rand_value) != arr.end()){
std::remove(arr.begin(), arr.end(), rand_value);
}
sort(arr.begin(), arr.end());
index = fibonacci_search(arr, rand_value);
passed = passed && (index == -1);
}
return passed;
}

/**
* @brief random tests which cover cases when we have one, multiple or zero occurences of the value we're looking for
*/
bool random_tests(){
bool passed = true;
int rand_num, rand_value, index, real_value, num_tests = 10000;
std::vector<int> arr;
while(num_tests--){
arr.clear();
for(int i = 0; i < 100; i++){
rand_num = std::rand() % 1000;
arr.push_back(rand_num);
}
rand_value = std::rand() % 1000;
std::sort(arr.begin(), arr.end());
index = fibonacci_search(arr, rand_value);
if(index != -1){
real_value = arr[index];
passed = passed && (real_value == rand_value);
} else {
passed = passed && (std::find(arr.begin(), arr.end(), rand_value) == arr.end());
}
}
return passed;
}

/**
* Main Function
* testing the algorithm
*/
int main() {
assert(no_occurence_tests());
assert(random_tests());
return 0;
}
``````