[알고리즘문제풀기] qr code

문제

내가 작성한 정답

String

class Solution {
    public String solution(int q, int r, String code) {
        String answer = "";
        for(int i=0; i<code.length(); i++){
            if(i%q==r) answer += code.charAt(i);
        }
        return answer;
    }
}

StringBuilder

// charAt
class Solution {
    public String solution(int q, int r, String code) {
        StringBuilder answer = new StringBuilder();
        for(int i=0; i<code.length(); i++){
            if(i%q==r) answer.append(code.charAt(i));
        }
        return answer.toString();
    }
}

// substring
class Solution {
    public String solution(int q, int r, String code) {
        StringBuilder answer = new StringBuilder();
        for(int i=0; i<code.length(); i++){
            if(i%q==r) answer.append(code.substring(i,i+1));
        }
        return answer.toString();
    }
}

// String[]
class Solution {
    public String solution(int q, int r, String code) {
        StringBuilder answer = new StringBuilder();
        String[] c = code.split("");
        for(int i=0; i<code.length(); i++){
            if(i%q==r) answer.append(c[i]);
        }
        return answer.toString();
    }
}
 
// char[]
class Solution {
    public String solution(int q, int r, String code) {
        StringBuilder answer = new StringBuilder();
        char[] c = code.toCharArray();
        for(int i=0; i<code.length(); i++){
            if(i%q==r) answer.append(c[i]);
        }
        return answer.toString();
    }
}

stream

// string
import java.util.stream.*;

class Solution {
    public String solution(int q, int r, String code) {
        return IntStream.range(0,code.length())
                .filter(i->i%q==r)
                .mapToObj(i->code.substring(i,i+1))
                .reduce("",String::concat);
    }
}

// char
import java.util.stream.*;

class Solution {
    public String solution(int q, int r, String code) {
        return IntStream.range(0,code.length())
                .filter(i->i%q==r)
                .mapToObj(i->""+code.charAt(i))
                .collect(Collectors.joining());
    }
}

다른 사람들의 정답

class Solution {
    public String solution(int q, int r, String code) {

        StringBuilder sb = new StringBuilder();

        for (int i = r; i < code.length(); i += q)
            sb.append(code.charAt(i));

        return sb.toString();
    }
}