Lesson 1 - BinaryGap

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].

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int를 이진수로 바꾸고 1과 1 사이에 있는 0의 최대 개수가 몇개인지 찾는 문제이다.
쉽게 풀었지만 binaryString을 charArray로 바꿔서 char를 int와 비교할 때 문제가 되었다.

class Solution {
    public int solution(int N) {
        String binaryString = Integer.toBinaryString(N);
        int result = 0;

        int maxLength = 0;
        
        char[] charArray = binaryString.toCharArray();

        for(int i=0; i<charArray.length; i++) {
            if((Character.getNumericValue(charArray[i])) == 1) {
                if(result < maxLength) {
                    result = maxLength;
                }                   
                maxLength = 0;                
            } else {
                maxLength++;                
             
            }
        }
        
        return result;
    }
}

왜냐 하면 char를 int로 형변환하는 경우에는 아스키코드가 출력이 된다.

char c = '1';
int n = (int)c;

System.out.println(n); // 9

아래 처럼 0을 뺴줘 계산하는 방법도 있고

char c = '1';
int n = (int)c - '0'; 49 - 48 = 1

System.out.println(n); // 1

Chracter 클래스의 함수를 쓰는 방법이 있다.

char c = '1';
int n = Character.getNumericValue(c);

System.out.println(n); // 1