Sorting

1. Sorting • List is rearranged into sorted order • How is the sorted order determined? • The ItemType is responsible for determining the key to be used in comparison of instances of the item. • The ItemType relational operator< determines the sorted order of the list. • To be really efficient, we also need a fast sort algorithm.

2. Common Sort Algorithms • Bubble Sort Heap Sort • Selection Sort Merge Sort • Insertion Sort Quick Sort • There are many known sorting algorithms. Bubble sort is the slowest, running in n2 time. Quick sort is the fastest, running in n lg n time. • As with searching, the faster the sorting algorithm, the more complex it tends to be.

3. Selection Sort • Selection sort algorithm: sorts a list by selecting the smallest element in the list and then moving this element to the top of the list • The first time we locate the smallest item in the entire list • The second time we locate the smallest item in the rest of the list starting, etc.

4. Selection Sort The approach of Selection Sort: • select one value and put it in its final place in the sort list • repeat for all other values In more detail: • find the smallest value in the list • switch it with the value in the first position • find the next smallest value in the list • switch it with the value in the second position • repeat until all values are placed

5. Selection Sort pass 1: 61 39 32 21 2 37 An example: sort the list 61, 39, 32, 21, 2, 37 pass 2: 2 39 32 21 61 37 pass 3: 2 21 32 39 61 37 pass 4: 2 21 32 39 61 37 pass 5: 2 21 32 37 61 39 result: 2 21 32 37 39 61

6. Selection Sort Routine void ListType::SelSort() { ItemType item; int passCount; int searchIndx; int minIndx; for (passCount = 0; passCount < length-1; passCount++) { minIndx = passCount; for (searchIndx = passCount+1; searchIndx<length; searchIndx++) if (data[searchIndx] < data[minIndx]) minIndx = searchIndx; item = data[minIndx]; data[minIndx] = data[passCount]; data[passCount] = item; } }