[Codility] Lesson1. BinaryGap (C++)

🔮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.

 

🔮풀이

 string 타입으로 이진수를 구한 후, 현재 문자가 '0'이고 이전 문자가 '1'이면 cnt를 증가.

다시 1을 발견하면 이전의 cnt값과 비교하여 가장 큰 값으로 answer 갱신.

answer가 초기값 -1에서 변화가 없다면 binary gap을 구할 수 없는 문자열이므로 0 return.

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🔮코드

#include <algorithm>
#include <iostream>
#include <vector>
#include <string>

int solution(int N) {
    string str = "";
    int answer = -1;

    while(N>0){
        if(N%2 == 1){
            str += '1';
        }
        else{
            str += '0';
        }
        N = N/2;
    }
    reverse(str.begin(), str.end());

    bool ok = false;
    int cnt = 0;
    int idx = 1;
    int size = str.size();
    while(idx < size){
        if(str[idx] == '0' && str[idx-1] == '1'){
            while(str[idx] == '0'){
                cnt++;
                idx++;
            }
            if(str[idx]=='1')
            {
                ok = true;
                answer = max(cnt,  answer);
            }
            cnt = 0;
            ok = false;
        }
        idx++;
    }
    if(answer == -1)
        answer = 0;
    return answer;
}