3. . Answer the questions regarding the following pro- gram import java.util.Arr
ID: 3574176 • Letter: 3
Question
3. . Answer the questions regarding the following pro- gram
import java.util.ArrayList;
public class Eratosthenes {
public static void main(String []args) {
ArrayList<Integer> al = new ArrayList<>();
int n = 120;
for(int i = 0; i < n; i++) {
al.add(1); }
al.set(0,0);
al.set(1,0);
for(int i = 2; i < n; i++) {
for(int j = 2; i*j < n; j++) {
al.set(i*j,0);
} }
for(int i = 0; i < n; i++) {
if (al.get(i) > 0) {
System.out.println(i);
}
} }
}
b : What are the common characteristics of the printed numbers. Explain brie y. ?
c : The following program execute the same algorithm as the above. Complete the following program.
import java.util.ArrayList;
public class Prime {
public static void main(String []args) {
ArrayList<Object> al = new ArrayList<>();
int n = 120;
for(int i = 0; i < n; i++) {
_________; }
___________;
___________;
for(int i = 2; i < n; i++) {
for(int j = 2; i*j < n; j++) {
_____________;
} }
for(int i = 0; i < n; i++) {
if (______________________) {
System.out.println(i);
}
} }
}
Explanation / Answer
answer a> The output of the code is :
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
101
103
107
109
113
answer b> the numbers in the list are prime numbers. The sieve of Eratosthenes is one of the most efficient ways to find all primes smaller than n when n is smaller than 10 million or so.
answer c> In order to find Prime numbers below is the code :
import java.util.ArrayList;
public class Prime {
public static void main(String []args) {
ArrayList<Object> al = new ArrayList<>();
int n = 120;
for(int i = 0; i < n; i++) {
__al.add(1)__; }
___al.set(0,0)__;
___al.set(1,0)___;
for(int i = 2; i < n; i++) {
for(int j = 2; i*j < n; j++) {
_____________;
} }
for(int i = 0; i < n; i++) {
if (_____al.get(i) > 0_____) {
System.out.println(i);
}
} }
}
feel free to ask if you have any doubt :)
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