sortingAlgorithms - CS202 Fundamentals of Computer Science...

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Unformatted text preview: 2/21/11 CS202 - Fundamentals of Computer Science II 1 Sorting • Sorting is a process that organizes a collection of data into either ascending or descending order. • An internal sort requires that the collection of data fit entirely in the computer’s main memory. • We can use an external sort when the collection of data cannot fit in the computer’s main memory all at once but must reside in secondary storage such as on a disk. • We will analyze only internal sorting algorithms. • Any significant amount of computer output is generally arranged in some sorted order so that it can be interpreted. • Sorting also has indirect uses. An initial sort of the data can significantly enhance the performance of an algorithm. • Majority of programming projects use a sort somewhere, and in many cases, the sorting cost determines the running time. • A comparison-based sorting algorithm makes ordering decisions only on the basis of comparisons. 2/21/11 CS202 - Fundamentals of Computer Science II 2 Sorting Algorithms • There are many sorting algorithms, such as: – Insertion Sort – Selection Sort – Bubble Sort – Merge Sort – Quick Sort • First three sorting algorithms are not so efficient, but last two are efficient sorting algorithms. • We have already discussed Insertion Sort and Merge Sort algorithms. 2/21/11 CS202 - Fundamentals of Computer Science II 3 Selection Sort • The list is divided into two sublists, sorted and unsorted , which are divided by an imaginary wall. • We find the biggest element from the unsorted sublist and swap it with the element at the end of the unsorted data. • After each selection and swapping, the imaginary wall between the two sublists move one element back, increasing the number of sorted elements and decreasing the number of unsorted ones. • Each time we move one element from the unsorted sublist to the sorted sublist, we say that we have completed a sort pass. • A list of n elements requires n-1 passes to completely rearrange the data . 2/21/11 CS202 - Fundamentals of Computer Science II 4 Selection Sort (cont.) Unsorted Sorted 2/21/11 CS202 - Fundamentals of Computer Science II 5 Selection Sort (cont.) typedef type-of-array-item DataType; void selectionSort(DataType theArray[], int n) { for (int last = n-1; last >= 1; --last) { int largest = indexOfLargest(theArray, last+1); swap(theArray[largest], theArray[last]); } } 2/21/11 CS202 - Fundamentals of Computer Science II 6 Selection Sort (cont.) int indexOfLargest(const DataType theArray[], int size) { int indexSoFar = 0; for(int currentIndex=1; currentIndex<size;++currentIndex) { if (theArray[currentIndex] > theArray[indexSoFar]) indexSoFar = currentIndex; } return indexSoFar; } -------------------------------------------------------- void swap(DataType &x, DataType &y) { DataType temp = x; x = y; y = temp; } 2/21/11 CS202 - Fundamentals of Computer Science II 7 Selection Sort -- Analysis • In general, we compare keys and move items (or exchange items) in a...
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sortingAlgorithms - CS202 Fundamentals of Computer Science...

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