[BOJ] 17413 단어 뒤집기 2

문제 

www.acmicpc.net/problem/17413

17413번: 단어 뒤집기 2

풀이

1) 비효율적 코드(1776ms)

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.*;
import java.util.StringTokenizer;
import java.util.Map.*;

public class Main {
    static ArrayList<String> list;
    static String reverse(String str){
        String reverse = "";
        for(int i=str.length()-1;i>=0;i--)
            reverse+=str.charAt(i);
        return reverse;
    }
    static boolean is_alpha(char ch){
        if(ch>='a' && ch<='z')
            return true;
        return false;
    }
    static boolean is_num(char ch){
        if(ch>='0' && ch<='9')
            return true;
        return false;
    }
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        StringBuilder sb = new StringBuilder();
        String str = br.readLine();
        Queue<String> queue = new LinkedList<>();
        int idx=0;
        while(idx<str.length()){
            char ch = str.charAt(idx);
            if(ch == '<'){
                String tmp = "";
                tmp+=ch;
                idx++;
                while(idx<str.length() && str.charAt(idx)!='>'){
                    tmp+= str.charAt(idx++);
                }
                tmp+=str.charAt(idx++);
                queue.add(tmp);
            }
            else if(is_num(ch)||is_alpha(ch)){
                String tmp = "";
                tmp+=ch;
                idx++;
                while(idx<str.length() && (is_num(str.charAt(idx))||is_alpha(str.charAt(idx)))){
                    tmp+= str.charAt(idx++);
                }
                queue.add(reverse(tmp));
            }
            else{
                queue.add(" ");
                idx++;
            }
        }
        while(!queue.isEmpty())
            sb.append(queue.remove());
        System.out.println(sb);
    }
}

2) 효율적인 코드