[백준 1935] 후위 표기식2 (C++/Java)

이건 후위표기식(1918)보다 더 쉽다.

피연산자 (이 문제에서는 대문자)가 나온다면 스택에 넣다가

연산자 (+,-,*,/)를 만나면 스택에서 2개의 데이터를 꺼내 연산자에 따라 계산하면 된다.

-C++

#include<iostream>
#include<stack>
using namespace std;
stack<double> st;
int arr[27];
int main(void){
    cin.tie(0); cout.tie(0);
    ios_base :: sync_with_stdio(false);
 
    int n; string str;
    cin >> n;
    cin >> str;
    for(int i=0; i<n; i++)
        cin >> arr[i];
    
    int size = str.length();
 
    char ch; double num1, num2;
    
    for(int i=0; i<size; i++){
        ch = str[i];
 
        if(ch=='+' || ch=='-' || ch=='*' || ch=='/'){
            num2=(double)st.top(); st.pop();
            num1=(double)st.top(); st.pop();
                
            if(ch=='+') st.push(num1+num2);
            else if(ch=='-') st.push(num1-num2);
            else if(ch=='*') st.push(num1*num2);
            else st.push(num1/num2);
        }
        else if('A'<=ch && ch <='Z'){
            st.push(arr[ch-'A']);
        }
    }
 
    double ans = st.top();
 
    cout << fixed;
    cout.precision(2);
    cout << ans;
 
    return 0;
}

- JAVA

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.Stack;
 
public class Main{
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb = new StringBuilder();
        Stack<Double> st = new Stack<Double>();
 
        int n = Integer.parseInt(br.readLine());
        Double[] arr = new Double[n];
        String str = br.readLine();
 
        for(int i=0; i<n; i++)
            arr[i] = Double.parseDouble(br.readLine());
        
        int size = str.length();
 
        char ch; Double num1, num2;
        for(int i=0; i<size; i++){
            ch = str.charAt(i);
 
            if(ch=='+' || ch=='-' || ch=='*' || ch=='/'){
                num2=st.pop(); num1=st.pop();
                
                if(ch=='+') st.push(num1+num2);
                else if(ch=='-') st.push(num1-num2);
                else if(ch=='*') st.push(num1*num2);
                else st.push(num1/num2);
            }
            else if('A'<=ch && ch <='Z')
                st.push(arr[ch-'A']);
        }
 
        System.out.print(String.format("%.2f",st.pop()));
    }
}