후위 표기식.java

// BOJ - 후위 표기식(1918)
// 스택

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Stack;


public class Main_1918 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb = new StringBuilder();

        char[] array = br.readLine().toCharArray();

        Stack<Character> stack = new Stack<>();

        for(int i=0;i<array.length;i++){
            char c = array[i];
            if(c == '+' || c == '-' || c == '*' || c == '/'){
                while (!stack.isEmpty() && priority(stack.peek()) >= priority(c)){
                    sb.append(stack.pop());
                }
                stack.push(c);
            } else if(c == '('){
                stack.push(c);
            } else if(c == ')'){
                while (!stack.isEmpty() && stack.peek() != '('){
                    sb.append(stack.pop());
                }
                stack.pop();
            } else {
                sb.append(c);
            }


        }

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

        System.out.println(sb.toString());

    }

    public static int priority(char c){
        if(c == '(' || c == ')'){
            return 0;
        } else if(c == '+' || c == '-'){
            return 1;
        } else if(c == '/' || c == '*'){
            return 2;
        }
        return -1;
    }
}