题目描述

blablabla

样例

blablabla

java 代码

import java.io.*;
import java.util.*;
import java.lang.*;
public class Main{
    public static Stack<Long> num = new Stack<>();
    public static Stack<Character> op = new Stack<>();
    public static HashMap<Character , Integer > pr = new HashMap<Character , Integer >()
    {{  put('+',1);
        put('-',1);
        put('*',2);
        put('/',2);}};
    public static void eval(){
        long b = num.peek();num.pop();//先读b再读a!
        long a = num.peek();num.pop();

        char ops = op.peek();op.pop();
        long x = 0;
        if(ops=='+') x=a+b;
        if(ops=='-') x=a-b;
        if(ops=='*') x=a*b;
        if(ops=='/') x=a/b;
        num.push(x);

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

        String str = br.readLine();
        for(int i = 0 ; i < str.length() ; i++ ){
            char t = str.charAt(i);
            if(Character.isDigit(t)){
                int j = i,x=0;
                while(j < str.length() && Character.isDigit(str.charAt(j))){
                    x = x*10 + (str.charAt(j++) - '0');

                }
                num.push ((long) x) ;
                i = j-1;
            }
            else if (t == '(') {op.push(t);}
            else if (t == ')'){
                while(op.size()!=0 && op.peek() != '(') eval();
                op.pop();
            }
            else {
                while(op.size()!=0 && op.peek() != '('&& pr.get(op.peek()) >= pr.get(t)) eval();//op.peek()可能是"("
                op.push(t);
            }
        }
        while(op.size() != 0) eval();
        System.out.println(num.peek());
    }
}