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Saturday, 21 January 2017

Chapter 22 Exercise 14, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

22.14 (Execution time for prime numbers) Write a program that obtains the execution time for finding all the prime numbers less than 8,000,000, 10,000,000, 12,000,000, 14,000,000, 16,000,000, and 18,000,000 using the algorithms in Listings 22.5–22.7.


public class Exercise14 {

 public static void main(String[] args) {
  int begin = 8_000_000;
  int end = 18_000_000;
  int step = 2_000_000;
  
  System.out.print("\t\t|");
  for (int n = begin; n <= end; n += step) {
   System.out.printf("%15d", n);
  }
  System.out.println();
  System.out.println("----------------|-------------------------------------------------------------------------------------------");
  System.out.print("Listing 24.4\t|");
  for (int n = begin; n <= end; n += step) {
   long startTime = System.currentTimeMillis();
   getPrime1(n);
   long endTime = System.currentTimeMillis();
   long executionTime = (endTime - startTime) / 1000;
   System.out.printf("%15d", executionTime);
  }
  System.out.println();
  System.out.println("----------------|-------------------------------------------------------------------------------------------");
  System.out.print("Listing 24.5\t|");
  for (int n = begin; n <= end; n += step) {
   long startTime = System.currentTimeMillis();
   getPrime2(n);
   long endTime = System.currentTimeMillis();
   long executionTime = (endTime - startTime) / 1000;
   System.out.printf("%15d", executionTime);
  }
  System.out.println();
  System.out.println("----------------|-------------------------------------------------------------------------------------------");
  System.out.print("Listing 24.6\t|");
  for (int n = begin; n <= end; n += step) {
   long startTime = System.currentTimeMillis();
   getPrime3(n);
   long endTime = System.currentTimeMillis();
   long executionTime = (endTime - startTime) / 1000;
   System.out.printf("%15d", executionTime);
  }

 }

 
 public static int getPrime1(int n) {
  int count = 0;
  int number = 2;
  while (number <= n) {
   boolean isPrime = true;
   for (int divisor = 2; divisor <= (int) (Math.sqrt(number)); divisor++) {
    if (number % divisor == 0) {
     isPrime = false; 
     break;
    }
   }
   if (isPrime) {
    count++;
   }
   number++;
  }
  return count;
 }
 
 public static int getPrime2(int n) {
  java.util.List<Integer> list = new java.util.ArrayList<Integer>();
  int count = 0;
  int number = 2;
  int squareRoot = 1;
  while (number <= n) {
   boolean isPrime = true;
   if (squareRoot * squareRoot < number)
    squareRoot++;
   for (int k = 0; k < list.size() && list.get(k) <= squareRoot; k++) {
    if (number % list.get(k) == 0) {
     isPrime = false;
     break;
    }
   }
   if (isPrime) {
    count++; 
    list.add(number);
   }
   number++;
  }
  return count;
 }
 
 public static int getPrime3(int n) {
  boolean[] primes = new boolean[n + 1];
  for (int i = 0; i < primes.length; i++) {
   primes[i] = true;
  }
  for (int k = 2; k <= n / k; k++) {
   if (primes[k]) {
    for (int i = k; i <= n / k; i++) {
     primes[k * i] = false;
    }
   }
  }
  int count = 0;
  for (int i = 2; i < primes.length; i++) {
   if (primes[i]) {
    count++;
   }
  }
  return count;
 }
}

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