Implement an immutable, iterable data type BinaryStrings in BinaryStrings.java t

Question

Implement an immutable, iterable data type BinaryStrings in BinaryStrings.java to systematically iterate over length-n binary strings.

import edu.princeton.cs.algs4.StdOut;
import java.util.Iterator;

// An immutable data type to systematically iterate over length-n binary
// strings.
public class BinaryStrings implements Iterable<String> {
private final int n; // need all binary strings of length n

// Construct an iterable BinaryStrings object given the length of binary
// strings needed.
public BinaryStrings(int n) {
...
}

// A BinaryStringsIterator object.
public Iterator<String> iterator() {
...
}
  
// Binary strings iterator.
private class BinaryStringsIterator implements Iterator<String> {
private int count = 0; // number of binary strings returned
private int p = 0; // current number

// Are there anymore length-n binary strings left to be iterated?
public boolean hasNext() {
...
}

// The next length-n binary string.
public String next() {
...
}
  
// Remove is not supported.
public void remove() {
// nothing to do
}

// The n-bit representation of x.
private String binary(int x) {
String s = Integer.toBinaryString(x);
int padding = n - s.length();
for (int i = 1; i <= padding; i++) {
s = "0" + s;
}
return s;
}
}

// Test client. [DO NOt EDIT]
public static void main(String[] args) {
int n = Integer.parseInt(args[0]);
for (String s : new BinaryStrings(n)) {
StdOut.println(s);
}
}

$ java BinaryStrings 4
0000
0001
0010
0011
0100
0101
0110
1000
1001
1010
1011
1100
1101
1110
1111

Explanation / Answer

import edu.princeton.cs.algs4.StdOut;
import java.util.Iterator;

public class BinaryStrings implements Iterable<String>
{
private final int n;

public BinaryStrings(int n)
{
this.n = n;
}

public Iterator<String> iterator()
{
return new BinaryStringsIterator();
}

private class BinaryStringsIterator implements Iterator<String>
{
private int count = 0;
private int p = 0;   
public boolean hasNext()
{
p = count;
return count < Math.pow(2, n);
}

public String next()
{
count = count + 1;
return binary(p);
}

public void remove()
{
// nothing to do  
}

  
private String binary(int x)
{
String s = Integer.toBinaryString(x);
int padding = n - s.length();
for (int i = 1; i <= padding; i++)
{
s = "0" + s;
}
return s;
}
}

  
public static void main(String[] args){

int n = Integer.parseInt(args[0]);
for (String s : new BinaryStrings(n))
{
StdOut.println(s);
}
}
}

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