cycle_sort.cpp

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#include <algorithm>  
#include <cassert>    
#include <cstdint>
#include <iostream>   
#include <vector>     
 
namespace sorting {
namespace cycle_sort {
template <typename T>
std::vector<T> cycleSort(const std::vector<T> &in_arr) {
    std::vector<T> arr(in_arr);
    for (int cycle_start = 0; cycle_start <= arr.size() - 1; cycle_start++) {
        // initialize item
        T item = arr[cycle_start];
 
        // Count the number of elements smaller than item, this  number is the
        // correct index of item.
        int pos = cycle_start;
        for (int i = cycle_start + 1; i < arr.size(); i++) {
            if (arr[i] < item) {
                pos++;
            }
        }
 
        // item is already in correct position
        if (pos == cycle_start) {
            continue;
        }
 
        // duplicate  elements
        while (item == arr[pos]) pos += 1;
        if (pos == cycle_start) {
            continue;
        } else {
            std::swap(item, arr[pos]);
        }
        // Rest of the  elements
        while (pos != cycle_start) {
            pos = cycle_start;
            // Find position where we put the element
            for (size_t i = cycle_start + 1; i < arr.size(); i++) {
                if (arr[i] < item) {
                    pos += 1;
                }
            }
            // duplicate  elements
            while (item == arr[pos]) pos += 1;
            if (item == arr[pos]) {
                continue;
            } else {
                std::swap(item, arr[pos]);
            }
        }
    }
    return arr;
}
}  // namespace cycle_sort
}  // namespace sorting
 
static void test() {
    // Test 1
    // [4, 3, 2, 1] return [1, 2, 3, 4]
    std::vector<uint32_t> array1 = {4, 3, 2, 1};
    std::cout << "Test 1... ";
    std::vector<uint32_t> arr1 = sorting::cycle_sort::cycleSort(array1);
    assert(std::is_sorted(std::begin(arr1), std::end(arr1)));
    std::cout << "passed" << std::endl;
 
    // [4.3, -6.5, -7.4, 0, 2.7, 1.8] return [-7.4, -6.5, 0, 1.8, 2.7, 4.3]
    std::vector<double> array2 = {4.3, -6.5, -7.4, 0, 2.7, 1.8};
    std::cout << "Test 2... ";
    std::vector<double> arr2 = sorting::cycle_sort::cycleSort(array2);
    assert(std::is_sorted(std::begin(arr2), std::end(arr2)));
    std::cout << "passed" << std::endl;
 
    // Test 3
    // [3, 3, 3, 3] return [3, 3, 3, 3]
    std::vector<uint32_t> array3 = {3, 3, 3, 3};
    std::cout << "Test 3... ";
    std::vector<uint32_t> arr3 = sorting::cycle_sort::cycleSort(array3);
    assert(std::is_sorted(std::begin(arr3), std::end(arr3)));
    std::cout << "passed" << std::endl;
 
    // [9, 4, 6, 8, 14, 3] return [9, 4, 6, 8, 14, 3]
    std::vector<uint32_t> array4 = {3, 4, 6, 8, 9, 14};
    std::cout << "Test 4... ";
    std::vector<uint32_t> arr4 = sorting::cycle_sort::cycleSort(array4);
    assert(std::is_sorted(std::begin(arr4), std::end(arr4)));
    std::cout << "passed" << std::endl;
}
 
int main() {
    test();  // execute the test
    return 0;
}