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Thursday, 25 August 2016

Chapter 7 Exercise 16, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

7.16 (Execution time) Write a program that randomly generates an array of 100,000 integers and a key. Estimate the execution time of invoking the linearSearch method in Listing 7.6. Sort the array and estimate the execution time of invoking the binarySearch method in Listing 7.7. You can use the following code template to obtain the execution time:

long startTime = System.currentTimeMillis();
perform the task;
long endTime = System.currentTimeMillis();
long executionTime = endTime - startTime; 



public class ProgrammingEx7_16 {
 
 public static void main(String[] args) {
  int[] array = new int[100000];
 
  // Generating random numbers to fill the array up
  for (int i = 0; i < array.length; i++) {
   array[i] = intRandom(0, 100000);
  }
 
  int key = intRandom(0, 100000);
  long startTime = System.currentTimeMillis();
  int i = linearSearch(array, key);
  long endTime = System.currentTimeMillis();
  long executionTime = endTime - startTime;
 
  System.out.println(startTime + "," + endTime);
 
  System.out.println("The key is " + key + " and it is now at " + i);
  System.out.println("The execution time for linear search is "
    + executionTime);
 
  startTime = System.currentTimeMillis();
  selectionSort(array);
  endTime = System.currentTimeMillis();
  executionTime = endTime - startTime;
   
  System.out.println("The execution time for selection sort is "
    + executionTime);
   
   
  startTime = System.currentTimeMillis();
  i =binarySearch(array, key);
  endTime = System.currentTimeMillis();
  executionTime = endTime - startTime;
   
  System.out.println("The key is " + key + " and it is at " + i);
  System.out.println("The execution time for binary search is "
    + executionTime);
 
 }
 
 public static int intRandom(int lowerBound, int upperBound) {
  return (int) (lowerBound + Math.random()
    * (upperBound - lowerBound + 1));
 }
 
 public static void selectionSort(int[] list) {
  for (int i = 0; i < list.length - 1; i++) {
   // Find the minimum in the list[i..list.length-1]
   int currentMin = list[i];
   int currentMinIndex = i;
 
   for (int j = i + 1; j < list.length; j++) {
    if (currentMin > list[j]) {
     currentMin = list[j];
     currentMinIndex = j;
    }
   }
 
   // Swap list[i] with list[currentMinIndex] if necessary
   if (currentMinIndex != i) {
    list[currentMinIndex] = list[i];
    list[i] = currentMin;
   }
  }
 }
 
 public static int linearSearch(int[] list, int key) {
  for (int i = 0; i < list.length; i++) {
   if (key == list[i])
    return i;
  }
  return -1;
 }
 
 /** Use binary search to find the key in the list */
 public static int binarySearch(int[] list, int key) {
  int low = 0;
  int high = list.length - 1;
 
  while (high >= low) {
   int mid = (low + high) / 2;
   if (key < list[mid])
    high = mid - 1;
   else if (key == list[mid])
    return mid;
   else
    low = mid + 1;
  }
 
  return -low - 1; // Now high < low
 }
 
}

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