[알고리즘문제풀기] 글자 이어 붙여 문자열 만들기

문제

내가 작성한 정답

String

class Solution {
    public String solution(String my_string, int[] index_list) {
        String answer = "";
        for(int i= 0; i<index_list.length;i++){
            answer += my_string.substring(index_list[i],index_list[i]+1);
        }
        return answer;
    }
}

StringBuilder

class Solution {
    public String solution(String my_string, int[] index_list) {
        StringBuilder answer = new StringBuilder();
        for(int i= 0; i<index_list.length;i++){
            answer.append(my_string.substring(index_list[i], index_list[i] + 1));
        }
        return answer.toString();
    }
}

StreamAPI

import java.util.stream.*;

class Solution {
    public String solution(String my_string, int[] index_list) {
        return IntStream.range(0,index_list.length)
                .mapToObj(i->my_string.substring(index_list[i],index_list[i]+1))
                .collect(Collectors.joining());
    }
}

import java.util.stream.Collectors;
import java.util.Arrays;

class Solution {
    public String solution(String my_string, int[] index_list) {
        return Arrays.stream(index_list)
                .mapToObj(i->my_string.substring(i,i+1))
                .collect(Collectors.joining());
    }
}

다른 사람들의 정답

charAt

class Solution {
    public String solution(String my_string, int[] index_list) {
        StringBuilder sb = new StringBuilder();
        for(int i : index_list){
            sb.append(my_string.charAt(i));
        }
        return sb.toString();
    }
}

StreamAPI

import java.util.*;
import java.util.stream.Collectors;

class Solution {
    public String solution(String myString, int[] indexList) {
        return Arrays.stream(indexList)
			        .mapToObj(operand -> String.valueOf(myString.charAt(operand)))
			        .collect(Collectors.joining());
    }
}