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ReverseBinaryNumber.java
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ReverseBinaryNumber.java
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/*
* Copyright (C) 2014 Pedro Vicente Gómez Sánchez.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.pedrovgs.problem71;
import com.github.pedrovgs.problem70.ReverseOrderOfBinaryNumber;
/**
* Given an integer passed as parameter, can you write a method to return the reverse binary
* number? The reverse binary number is defined like the number where every 1 in the original
* number has a 0 in the reversed number and the same with 0 in the original number.
*
* For example:
*
* Input: 63 = 111111
* Output: 0
*
* Input = 5 = 101
* Output = 2 = 010
*
* @author Pedro Vicente Gómez Sánchez.
*/
public class ReverseBinaryNumber {
private ReverseOrderOfBinaryNumber reverseOrder;
public ReverseBinaryNumber() {
reverseOrder = new ReverseOrderOfBinaryNumber();
}
/**
* Iterative algorithm based on binary operators. The key of this algorithm is take in to account
* the number of digits of the binary representation. First we are going to create the reverse
* number with a 1 as first binary number. Then we are going to revert the order of the binary
* number and at the end we are going to remove the first one we added to take into account the
* number of digits of this binary number. The complexity order of this algorithm in space terms
* is O(1) and in time terms is equals to O(N) where N is the number of digits in the binary
* representation.
*/
public int reverse(int input) {
int result = 1;
do {
result <<= 1;
result |= (input & 1) == 1 ? 0 : 1;
input >>= 1;
} while (input != 0);
result = reverseBitsOrder(result);
result = removeFirstOne(result);
return result;
}
private int removeFirstOne(int number) {
return number >> 1;
}
private int reverseBitsOrder(int number) {
return reverseOrder.reverse(number);
}
}