Download
1 / 26
260 likes | 336 Vues
Fundamentals of Programming Session 17. Fall 2013. Instructor: Reza Entezari-Maleki Email: entezari@ce.sharif.edu. These slides have been created using Deitel’s slides . Sharif University of Technology . Outlines . Sorting Arrays Searching Arrays. Sorting Arrays .
E N D
Fundamentals of Programming Session 17 Fall 2013 • Instructor: Reza Entezari-Maleki • Email:entezari@ce.sharif.edu • These slides have beencreated using Deitel’s slides Sharif University of Technology
Outlines • Sorting Arrays • Searching Arrays
Sorting Arrays • Sorting data (i.e., placing the data into a particular order such as ascending or descending) is one of the most important computing applications. • Sorting data • Important computing application • Virtually every organization must sort some data • Massive amounts must be sorted • Sorting: an operation that segregates items into groups according to specified criterion. • A = { 3 1 6 2 1 3 4 5 9 0 } • A = { 0 1 1 2 3 3 4 5 6 9 }
Sorting Arrays … • There are many different types of sorting algorithms, but the primary ones are: • Bubble Sort • Selection Sort • Insertion Sort • Merge Sort • Quick Sort • Shell Sort • Heap Sort • Radix Sort • Swap Sort • ...
Bubble sort • Bubble sort (sinking sort) • Several passes through the array • Successive pairs of elements are compared • If increasing order (or identical), no change • If decreasing order, elements exchanged • Repeat these steps for every element
Bubble sort … • Example: • Go left to right, and exchange elements as necessary • One pass for each element • Original: 3 4 2 7 6 • Pass 1: 3 2 46 7(elements exchanged) • Pass 2: 2 34 6 7 • Pass 3: 2 3 4 6 7 (no changes needed) • Pass 4: 2 3 4 6 7 • Small elements "bubble" to the top (like 2 in this example)
Bubble sort … • Swapping variables int x = 3, y = 4; y = x; x = y; • What happened? • Both x and y are 3! • Need a temporary variable • Solution int x = 3, y = 4, temp = 0; temp = x; // temp gets 3 x = y; // x gets 4 y = temp; // y gets 3 • Figure 6.15 sorts the values in the elements of the 10-element array a into ascending order.
Selection sort • Selection sort • This type of sorting is called "Selection Sort" because it works by repeatedly element. • It works as follows: • First find the smallest in the array and exchange it with the element in the first position, • then find the second smallest element and exchange it with the element in the second position, • and continue in this way until the entire array is sorted.
Selection sort … • Pseudocode of selection sort SELECTION_SORT (A) 1. Fori ← 0 ton-2do2. minj ← i;3. minx ← A[i]4. Forj ← i + 1 to n do5. If A[j] < minx then6. minj ← j7. minx ← A[j]8. A[minj] ← A [i]9. A[i] ← minx
Insertion sort • Insertion sort algorithm somewhat resembles selection sort. • Array is imaginary divided into two parts: sorted one and unsorted one. • At the beginning, sorted part contains first element of the array and unsorted one contains the rest. • At every step, algorithm takes first element in the unsorted part and inserts it to the right place of the sorted one. • When unsorted part becomes empty, algorithm stops.
Insertion sort … • Pseudocode of selection sort INSERTION_SORT (A) 1. FOR j ← 1 TO length[A] 2. DO key ← A[j] 3. {Put A[j] into the sorted sequence A[1 . . j − 1]} 4. i ← j − 1 5. WHILEi > 0 and A[i] > key6. DOA[i +1] ← A[i] 7. i ← i − 1 8. A[i + 1] ← key
Searching Arrays • It may be necessary to determine whether an array contains a value that matches a certain key value. • The process of finding a particular element of an array is called searching. • In this section we discuss two searching techniques—the simple linear search technique and the more efficient (but more complex) binary search technique. • The linear search (Fig. 6.18) compares each element of the array with the search key.
