Negate a negative based binary (base -2) using Two's Complement Annotation.

NegaBinary.java

package com.codility.tasks;

/* 
  Negate a negative based binary (base -2) using Two's Complement Annotation.
  Given a base -2 number splitted into a primitive array of ints (int[]), return it's negation.
  
  EXAMPLES:
      INPUT:    [0,1,0,0,1,1,1]   // Decimal 39.
      OUTPUT:   [1,0,1,1,0,0,1]   // Decimal -39.
      
      INPUT:    [1,0,0,1,0,1,1]   // Decimal -53.
      OUTPUT:   [0,1,1,0,1,0,1]   // Decimal 53.
      
*/

import java.util.Arrays;

/*
  @author Arthur Alves < hello@arthuralves.com >
*/

public class NegaBinary {
  
  public static void main(String[] args) {

	int[] binary = new int[]{0,1,0,0,1,1,1}; // Decimal 39
  	System.out.println("Negation: "+Arrays.toString(solution(binary)));
  	
  }
  
  public static int fromBinaryToInt(int B[]) {
  
  	String stringBinary = "";
  	for (int digit: B) {
  		stringBinary = stringBinary + digit;
  	}
  	long l = Long.parseLong(stringBinary, 2);
	int i = (int) l;

  	return i;
  }
    
  public static int[] fromIntToBinary(int value, int size) {
    
  	String binaryString = Integer.toBinaryString(value);
  	binaryString = binaryString.substring(binaryString.length()-size);
  	int[] binaryArray = new int[binaryString.length()];
  	for (int i=0; i< binaryString.length(); i++) {
  		binaryArray[i] = (int)Long.parseLong(binaryString.substring(i, i+1));
  	}
	
  	return binaryArray;
  }

  public static int[] solution(int[] A) {
  	int value = fromBinaryToInt(A);
  	return fromIntToBinary(-value, A.length);
  }
  
}