sorting Namespace Reference

Sorting algorithms. More...

Functions
template<class Iterator >
void	merge (Iterator l, Iterator r, const Iterator e, char b[])
	merges 2 sorted adjacent segments into a larger sorted segment More...
template<class Iterator >
void	non_recursive_merge_sort (const Iterator first, const Iterator last, const size_t n)
	bottom-up merge sort which sorts elements in a non-decreasing order More...
template<class Iterator >
void	non_recursive_merge_sort (const Iterator first, const size_t n)
	bottom-up merge sort which sorts elements in a non-decreasing order More...
template<class Iterator >
void	non_recursive_merge_sort (const Iterator first, const Iterator last)
	bottom-up merge sort which sorts elements in a non-decreasing order More...
int	partition (int arr[], int low, int high)
void	quickSort (int arr[], int low, int high)
template<typename T >
void	shell_sort (T *arr, size_t LEN)
template<typename T , size_t N>
void	shell_sort (T(&arr)[N])
template<typename T >
void	shell_sort (std::vector< T > *arr)

Detailed Description

Sorting algorithms.

Function Documentation

merge()

template<class Iterator >

void sorting::merge	(	Iterator	l,
		Iterator	r,
		const Iterator	e,
		char	b[]
	)

merges 2 sorted adjacent segments into a larger sorted segment

best-case = worst-case = O(n)

Parameters

l	points to the left part
r	points to the right part, end of left part
e	points to end of right part
b	points at the buffer

                                                               {
    // create 2 pointers to point at the buffer
    auto p(reinterpret_cast<std::remove_reference_t<decltype(*l)>*>(b)), c(p);
    // move the left part of the segment
    for (Iterator t(l); r != t; ++t) *p++ = std::move(*t);
    // while neither the buffer nor the right part has been exhausted
    // move the smallest element of the two back to the container
    while (e != r && c != p) *l++ = std::move(*r < *c ? *r++ : *c++);
    // notice only one of the two following loops will be executed
    // while the right part hasn't bee exhausted, move it back
    while (e != r) *l++ = std::move(*r++);
    // while the buffer hasn't bee exhausted, move it back
    while (c != p) *l++ = std::move(*c++);
}

Here is the call graph for this function:

non_recursive_merge_sort() [1/3]

template<class Iterator >

void sorting::non_recursive_merge_sort	(	const Iterator	first,
		const Iterator	last
	)

bottom-up merge sort which sorts elements in a non-decreasing order

Parameters

first	points to the first element
last	points to 1-step past the last element

                                                                         {
    non_recursive_merge_sort(first, last, last - first);
}

Here is the call graph for this function:

non_recursive_merge_sort() [2/3]

template<class Iterator >

void sorting::non_recursive_merge_sort	(	const Iterator	first,
		const Iterator	last,
		const size_t	n
	)

bottom-up merge sort which sorts elements in a non-decreasing order

sorts elements non-recursively by breaking them into small segments, merging adjacent segments into larger sorted segments, then increasing the sizes of segments by factors of 2 and repeating the same process. best-case = worst-case = O(n log(n))

Parameters

first	points to the first element
last	points to 1-step past the last element
n	the number of elements

                                              {
    // create a buffer large enough to store all elements
    // dynamically allocated to comply with cpplint
    char* buffer = new char[n * sizeof(*first)];
    // buffer size can be optimized to largest power of 2 less than n
    // elements divide the container into equally-sized segments whose
    // length start at 1 and keeps increasing by factors of 2
    for (size_t length(1); length < n; length <<= 1) {
        // merge adjacent segments whose number is n / (length * 2)
        Iterator left(first);
        for (size_t counter(n / (length << 1)); counter; --counter) {
            Iterator right(left + length), end(right + length);
            merge(left, right, end, buffer);
            left = end;
        }
        // if the number of remaining elements (n * 2 % length) is longer
        // than a segment, merge the remaining elements
        if ((n & ((length << 1) - 1)) > length)
            merge(left, left + length, last, buffer);
    }
    delete[] buffer;
}

Here is the call graph for this function:

non_recursive_merge_sort() [3/3]

template<class Iterator >

void sorting::non_recursive_merge_sort	(	const Iterator	first,
		const size_t	n
	)

bottom-up merge sort which sorts elements in a non-decreasing order

Parameters

first	points to the first element
n	the number of elements

                                                                    {
    non_recursive_merge_sort(first, first + n, n);
}

Here is the call graph for this function:

partition()

int sorting::partition	(	int	arr[],
		int	low,
		int	high
	)

This function takes last element as pivot, places the pivot element at its correct position in sorted array, and places all smaller (smaller than pivot) to left of pivot and all greater elements to right of pivot

                                            {
    int pivot = arr[high];  // taking the last element as pivot
    int i = (low - 1);      // Index of smaller element
 
    for (int j = low; j < high; j++) {
        // If current element is smaller than or
        // equal to pivot
        if (arr[j] <= pivot) {
            i++;  // increment index of smaller element
            int temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
    }
    int temp = arr[i + 1];
    arr[i + 1] = arr[high];
    arr[high] = temp;
    return (i + 1);
}

quickSort()

void sorting::quickSort	(	int	arr[],
		int	low,
		int	high
	)

The main function that implements QuickSort arr[] --> Array to be sorted, low --> Starting index, high --> Ending index

                                             {
    if (low < high) {
        int p = partition(arr, low, high);
        quickSort(arr, low, p - 1);
        quickSort(arr, p + 1, high);
    }
}

Here is the call graph for this function:

shell_sort() [1/3]

template<typename T >

void sorting::shell_sort

(

std::vector< T > *

arr

)

function overload - when input array is of type std::vector, simply send the data content and the data length to the above function.

                                   {
    shell_sort(arr->data(), arr->size());
}

Here is the call graph for this function:

shell_sort() [2/3]

template<typename T >

void sorting::shell_sort	(	T *	arr,
		size_t	LEN
	)

Optimized algorithm - takes half the time by utilizing Mar

                                    {
    const unsigned int gaps[] = {701, 301, 132, 57, 23, 10, 4, 1};
    const unsigned int gap_len = 8;
    size_t i, j, g;
 
    for (g = 0; g < gap_len; g++) {
        unsigned int gap = gaps[g];
        for (i = gap; i < LEN; i++) {
            T tmp = arr[i];
 
            for (j = i; j >= gap && (arr[j - gap] - tmp) > 0; j -= gap) {
                arr[j] = arr[j - gap];
            }
 
            arr[j] = tmp;
        }
    }
}

shell_sort() [3/3]

template<typename T , size_t N>

void sorting::shell_sort

(

T(&)

arr[N]

)

function overload - when input array is of a known length array type

                             {
    shell_sort(arr, N);
}

Here is the call graph for this function: