배열

1. 문자열을 정수로 바꾸는 방법

class Solution {
    public int solution(String s) {
        return Integer.parseInt(s);
    }
}

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2. 정수의 각 자릿수를 큰것부터 작은 순으로 정렬한 새로운 정수를 리턴하는 법

class Solution {
    public long solution(long n) {
        char[] arr = String.valueOf(n).toCharArray();
        java.util.Arrays.sort(arr);
        return Long.parseLong(new StringBuilder(new String(arr)).reverse().toString());
    }
}

 

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3. 배열중에 특정 문자열이 들어간 인덱스를 찾는 법

class Solution {
    public String solution(String[] seoul) {

        for (int i = 0; i < seoul.length; i++) {
            if (seoul[i].equals("Kim")) {
                return "김서방은 " + i + "에 있다";
            }
        }
        return "김서방을 찾을 수 없습니다.";
    }
}

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4. 조건에 맞는 인덱스만 남겨서 오름차순으로 새로운 배열에 넣어주는 방법

class Solution {
    public int[] solution(int[] arr, int divisor) {
        int[] answer = Arrays.stream(arr)
            .filter(n -> n % divisor == 0)
            .sorted()
            .toArray();
        
        return answer.length == 0 ? new int[]{-1} : answer;
    }
}

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5. 문자열에서 특정 부분을 다른 문자로 수정하고싶을 때

class Solution {
    public String solution(String phone_number) {
        String answer = "";
        
        char[] arr = phone_number.toCharArray();
        
        for (int i = 0; i < arr.length - 4; i++){
            arr[i] = '*';
        }
        
        return new String(arr);
    }
}

 

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