4. 단어 뒤집기

import java.util.*;

class Main {
	public String solution(String str) {
		String answer = "";
		for(int i=str.length()-1; i>= 0; i--) {
			answer = answer.concat(Character.toString(str.charAt(i)));	
		}
		return answer;
	}

	public static void main(String[] args) {
		Main T = new Main();
		Scanner kb = new Scanner(System.in);
		int num = kb.nextInt();
		String[] s = new String[num];
		for(int i =0; i< num; i++) {
			s[i] = kb.next();
		}
		for(int i=0; i<num; i++) {
			System.out.println(T.solution(s[i]));
		}
	}
}

 

 

 

 

import java.util.*;

class Main {
	public ArrayList<String> solution(String[] str) {
		ArrayList<String> answer = new ArrayList<>();
		for (String x : str) {
			String tmp = new StringBuilder(x).reverse().toString();
			answer.add(tmp);
		}

		return answer;
	}

	public static void main(String[] args) {
		Main T = new Main();
		Scanner kb = new Scanner(System.in);
		int num = kb.nextInt();
		String[] s = new String[num];
		for (int i = 0; i < num; i++) {
			s[i] = kb.next();
		}

		for (String x : T.solution(s)) {
			System.out.println(x);
		}

	}
}

StringBuilder. String객체는 수정하면 새로 만들어지기 때문에 String 연산이 많은 경우 StringBuilder클래스를 사용하여 String조작을 함. StringBuilder toString(), reverse()를 이용한 방법

ArrayList<String>

 

 

import java.util.*;

class Main {
	public ArrayList<String> solution(String[] str) {
		ArrayList<String> answer = new ArrayList<>();

		for (String x : str) {
			char[] s = x.toCharArray();
			int lt = 0, rt = x.length() - 1;
			while (lt < rt) {
				char tmp = s[lt];
				s[lt] = s[rt];
				s[rt] = tmp;
				lt++;
				rt--;
			}
			String tmp = String.valueOf(s);
			answer.add(tmp);
		}
		return answer;
	}

	public static void main(String[] args) {
		Main T = new Main();
		Scanner kb = new Scanner(System.in);
		int num = kb.nextInt();
		String[] s = new String[num];

		for (int i = 0; i < num; i++) {
			s[i] = kb.next();
		}

		for (String x : T.solution(s)) {
			System.out.println(x);
		}

	}
}

lt, rt

toCharArray()

String클래스의 static메소드 valueOf()