Lesson1. Binary Gap

https://app.codility.com/programmers/lessons/1-iterations/

 

문제 : 

A binary gap within a positive integer N is any maximal sequence of consecutive zeros that is surrounded by ones at both ends in the binary representation of N.

For example, number 9 has binary representation 1001 and contains a binary gap of length 2. The number 529 has binary representation 1000010001 and contains two binary gaps: one of length 4 and one of length 3. The number 20 has binary representation 10100 and contains one binary gap of length 1. The number 15 has binary representation 1111 and has no binary gaps. The number 32 has binary representation 100000 and has no binary gaps.

Write a function:

class Solution { public int solution(int N); }

that, given a positive integer N, returns the length of its longest binary gap. The function should return 0 if N doesn't contain a binary gap.

For example, given N = 1041 the function should return 5, because N has binary representation 10000010001 and so its longest binary gap is of length 5. Given N = 32 the function should return 0, because N has binary representation '100000' and thus no binary gaps.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [1..2,147,483,647].

 

 

- 자연수 N을 받아 이진수로 변환하고, 

- 1과 1사이에 있는 최대 0의 count를 구하는 문제

- 1과 1사이에 있는 0이 없다면 0를 출력함.

 

package codility.num1;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Solution {
    public int solution(int N) {
        // input : natural number n between 1 and 2,147,483,647
        // output : the length of '0' between '1' and '1' , if 0 between 1 and 1 not exists, just print '0'

        List<Integer> answerList = new ArrayList<>();
        int answer = 0;

        // 1. change number into binary
        String binary = Integer.toBinaryString(N);

        // 2. change string to char array
        char[] binaryArr = binary.toCharArray();

        // 3. check the length of binaryArr is one or two, just print '0'
        if (binaryArr.length == 1 || binaryArr.length == 2)
            return answer;

        List<Integer> oneArr = new ArrayList<>();

        for (int i = 0; i < binaryArr.length; i++) {
            if (binaryArr[i] == '1')
                oneArr.add(i);
        }

        for (int i = oneArr.size() - 1; i > 0; i--) {
            int zeroCount = oneArr.get(i) - oneArr.get(i - 1) - 1;
            answerList.add(zeroCount);
        }

        if (!(answerList.size() == 0))
            answer = Collections.max(answerList);

        return answer;
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int n = Integer.parseInt(br.readLine());

        Solution sol = new Solution();
        System.out.println(sol.solution(n));
    }
}