백준 1992번: 쿼드트리

문제 출처: https://www.acmicpc.net/problem/1992

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
public class Main {
    private static String[] arr;
    
    public static void main(String[] args) throws IOException {
        BufferedReader reader= new BufferedReader(new InputStreamReader(System.in));
        
        int N = Integer.parseInt(reader.readLine());
        arr = new String[N];
        for(int i=0 ; i<N ; i++)
            arr[i] = reader.readLine();
        
        if(N == 1)
            System.out.println(arr[0]);
        else 
            System.out.println(quad_tree(0, N-1, 0, N-1));
    }
    
    public static String quad_tree(int xLow, int xHigh, int yLow, int yHigh){
        StringBuilder str = new StringBuilder();
        
        if(xLow < xHigh && yLow < yHigh){
            int xMid = (xLow+xHigh)/2;
            int yMid = (yLow+yHigh)/2;
            
            String one = quad_tree(xLow, xMid, yLow, yMid);
            String two = quad_tree(xMid+1, xHigh, yLow, yMid);
            String three = quad_tree(xLow, xMid, yMid+1, yHigh);
            String four = quad_tree(xMid+1, xHigh, yMid+1, yHigh);
            
            if(one.equals("")){
                str.append(arr[yLow].charAt(xLow));
                str.append(arr[yLow].charAt(xHigh));
                str.append(arr[yHigh].charAt(xLow));
                str.append(arr[yHigh].charAt(xHigh));
            } else {
                str.append(one + two + three + four);
            }
            
            if(str.toString().equals("0000"))
                str = new StringBuilder("0");
            else if(str.toString().equals("1111"))
                str = new StringBuilder("1");
            else
                str = new StringBuilder("("+str+")");
        }
        return str.toString();
    }
}