[백준] 203 - 자료구조 1 (참고) : 후위 표기식 (1918번 JAVA)

[백준] 203 - 자료구조 1 (참고) : 후위 표기식 (1918번 JAVA)

 

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.EmptyStackException;
import java.util.Stack;

public class Main{
    
    public static void main(String[] args) throws IOException, EmptyStackException{

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        Stack<Character> stack = new Stack<>();
        StringBuilder sb = new StringBuilder();
        
        // 계산식
        String str = br.readLine(); 

        for(int i=0; i<str.length(); i++){

            // A ~ Z
            if( (int)str.charAt(i) >= 65 && (int)str.charAt(i)<=90 ){
                sb.append(str.charAt(i));
            }

            else {
                switch (str.charAt(i)) {
                    case '(':
                        stack.push(str.charAt(i));
                        break;

                    case ')':
                        char x;
                        while(true){
                            x = stack.pop();
                            if (x == '('){
                                break;
                            }
                            else {
                                sb.append(x);
                            }
                        }
                        break;

                    case '+': case '-':
                        if(!stack.isEmpty()){
                            while (!stack.isEmpty() && (stack.peek() == '+' || stack.peek() == '-' || stack.peek() == '*' || stack.peek() == '/')){
                                sb.append(stack.pop());
                            }
                        }
                        stack.push(str.charAt(i));
                        break;

                    case '*': case '/':
                        if(!stack.isEmpty()){
                            while (!stack.isEmpty() && (stack.peek() == '*' || stack.peek() == '/')){
                                sb.append(stack.pop());
                            }
                        }
                        stack.push(str.charAt(i));
                        break;

                } // switch 
            } // else
        } // for

        while(!stack.isEmpty()){
            sb.append(stack.pop());
        }

        bw.write(sb.toString());
        bw.flush();
        bw.close();
    }
}

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