Sorting Algorithms Report

International academy for engineering and media science

FACULTY OF ENGINEERING ELECTRICAL ENGINEERING DEPARTMENT Communication major.

Report Sorting algorithms. Data structures & Algorithms.

Supervisor: D. Mostafa El sayed

Prepared by: NADA TAWFICK 

Table of Contents

Abstract ................................ ................................ ................................ ..................... 2 Classification of sorting algorithms ........................... ..... ................................ ............ 3 Popular sorting algorithms ............................ .... ................................ ......................... 4 1.Bubble sort .......................... ...... ................................ .......................... ...... ..............

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2. Selection sort................................ ................................ ................................ .......... 4 3.Insertion sort 5 4.Shell sort.6 5.Quick sort..7 comparison between sorting algorithms8

LIST OF TABLES

Table ( 1):Comparison of sorting algorithms ................................ ........................... ... 8 Table (2): Sorting timing. ................................ ........................... ..... ........................... 8

LIST OF FIGURES

Figure (1.1): Insertion sort. ............................ .... ................................ ......................... 5 Figure (2.1): Shell sort. ........................... ..... ................................ ........................... ... 6 Figure (3.1): Quick sort ........................... ..... ................................ ........................... ... 7

Abstract In computer science, a sorting algorithm is an algorithm that puts elements of a list in a certain order. The most-used orders are numerical order . Efficient sorting is important for optimizing the use of other algorithms (such as search and merge algorithms) that require sorted lists to work correctly; it is also often useful for canonicalizing data and for producing human-readable output. More formally, the output must satisfy two conditions, 1-The output is in nondecreasing order (each element is no smaller than the previous element according to the desired total order. 2-The output is a permutation, or reordering, of the input. Since the dawn of computing, the sorting problem h as attracted a great deal of research, perhaps due to the complexity of solving it efficiently despite its simple, familiar statement. For example, bubble sort was analyzed as early as 1956.Although many consider it a solved problem, useful new sorting algorithms are still being invented (for example, library sort was first published in 2004). Sorting algorithms are prevalent in introductory computer science classes, where the abundance of  algorithms for the problem provides a gentle introduction to a varie ty of  core algorithm concepts, such as big O notation, divide and conquer algorithms, data structures, randomized algorithms, best, worst and average case analysis, time-space tradeoffs, and lower bounds.

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Sorting algorithms: The methods followed in arranging a set of data items into a sequence according to precise rules.

Classification: Sorting algorithms used in computer science are often classified by :

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Computational complexity (worst, av erage and best behaviour) of element comparisons in terms of the size of the list (n). For typical sorting algorithms good behavior is O(n log n) and bad behavior is (n²). (See Big O notation) Ideal behavior for a sort is O(n). Sort algorithms which only use an abstract key comparison operation always need (n log n) comparisons in the worst case.

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Computational complexity of swaps (for "in place" algorithms) .

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Memory usage (and use of other computer resources). In particular, some sorting algorithms are "in place", such that only O(1) or O(log n) memory is needed beyond the items being sorted, while others need to create auxiliary locations for data to be temporarily stored.

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Recursion.

Some algorithms are either recursive or non recursive, while others

may be both (e.g., merge sort). o

Stability: stable sorting algorithms maintain the relative order of records with equal keys(i.e., values).

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Whether

or not they are a comparison sort. A compari son sort examines the data

only by comparing two elements with a comparison operator.

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General method: insertion, exchange, selection, merging,

etc. Exchange sorts

include bubble sort and quicksort. Selection sorts include shaker sort and heapsort.

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Popular sorting algorithms. 1-Bubble sort Bubble sort is a straightforward and simplistic method of sorting data that is used in computer science education. The algorithm starts at the beginning of the data set. It compares the first two elements, and if the first is greater than the second, it swaps them. It continues doing this for each pair of adjacent elements to the end of the data set. It then starts again with the first two elements, repeating until no swaps have occurred on the last pass.

While

simple, this algorithm is highly

inefficient and is rarely used except in education. A slightly better variant, cocktail sort, works by inverting the ordering criteria and the pass direction on alternating passes. Its average case and worst case are both O(n²).

2-Selection sort Selection sort is a simple sorting algorithm that improves on the performance of bubble sort. It works by first finding the smallest element using a linear scan and swapping it into the first position in the list, then finding the second smallest element by scanning the remaining elements, and so on. Selection sort is unique compared t o almost any other algorithm in that its running time is not affected by the prior ordering of the list: it performs the same number of operations because of its simple structure. Selection sort requires (n - 1) swaps and hence (n) memory writes. However, Selection sort requires (n - 1) + (n - 2) + ... + 2 + 1 = n(n - 1) / 2 = (n2) comparisons. Thus it can be very attractive if  writes are the most expensive operation, but otherwise selection sort will usually be outperformed by insertion sort or the more complicated algorithms.

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3-Insertion sort Insertion sort is a simple sorting algorithm that is relatively efficient for small lists and mostly-sorted lists, and often is used as part of more sophisticated algorithms. It works by taking elements from the list one by one and inserting them in their correct position into a new sorted list. In arrays, the new list and the remaining elements can share the array's space, but insertion is expensive, requiring shifting all following elements over by one. The insertion sort works just like its name suggests - it inserts each item into its proper place in the final list. The simplest implementation of this requires two list structures - the source list and the list into which sorted items are inserted. To save memor y, most implementations use an in-place sort that works by moving the current item past the already sorted items and repeatedly swapping it with the preceding item until it is in place. Shell sort (see below) is a variant of insertion sort that is more efficient for larger lists. This method is much more efficient than the bubble sort, though it has more constraints. .

Figure 1-1: insertion sort

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4-Shell sort

Shell sort was invented by Donald Shell in 1959. It improves upon bubble sort and insertion sort by moving out of order elements more than one position at a time. One implementation can be described as arranging the data sequence in a two-dimensional array and then sorting the columns of the array using insertion sort. Although this method is inefficient for large data sets, it is one of the fastest algorithms for sorting small numbers of elements (sets with less than 1000 or so elements). Another advantage of this algorithm is that it requires relatively small amounts of memory.

figure 2-1:shell sort.

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5-Quicksort Quicksort is a divide and conquer algorithm which relies on a partition operation: to partition an array, we choose an element, called a pivot, move all smaller elements before the pivot, and move all greater elements after it. This can be done efficiently in linear time and in -place. We

then recursively sort the lesser and greater sublists. Efficient

implementations of quicksort (with in-place partitioning) are typically unstable sorts and somewhat complex, but are among the fas test sorting algorithms in practice. Together with its modest O(log n) space usage, this makes quicksort one of the most popular sorting algorithms, available in many standard libraries. The most complex issue in quicksort is choosing a good pivot element; consistently poor choices of pivots can result in drastically slower (O(n²)) performance, but if at each step we choose the median as the pivot then it works in O(n log n)

Figure 3-1: Quick sort .

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Comparison In this section we will compare the sorting algorithms covered: insertion sort, shell sort, and quicksort. There are several fact ors that influence the choice of a sorting algorithm:

Stable sort. Recall that a stable sort will leave identical keys in the same relative position in the sorted output. I nsertion sort is the only algorithm covered that is stable. Space. An in-place sort does not require any extra space to accomplish its task. Both insertion sort and shell sort are in- place sorts. Quicksort requires stack space for  recursion, and therefore is not an in-place sort. Tinkering with the algorithm considerably reduced the amount of time required.

Time. The time requi red to sort a dataset can easily become astronomic al Table 12shows the relative timings for each method. The ti me required to sort a randomly ordered dataset is shown in Table 1-2 Simplicity. The number of statements required for each algorithm may be found i n Table 11Simpler algorithms result in f ewer programming errors.

. Table( 1) comparison of sorting methods.

Table (2) sort timings.

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