PTA练习题：表达式求值_1

2023-03-14 13:53 9阅读 0赞

在一个表达式中，只有“(”，“)”，“0-9”，“+”，“-”，“\*”，“/”，“^”，请求出表达式的值。(“/”用整数除法)。

输入格式:

共1 行，为一个算式。 （算式长度<=30 其中所有数据在 0~2^31-1的范围内）。

输出格式:

共一行，为表达式的值。

输入样例:

在这里给出一组输入。例如：

1+(3+2)*(7^2+6*9)/(2)  
输出样例:

在这里给出相应的输出。例如：

258

import java.util.Scanner;
    import java.util.Stack;
    
    public class Main {
        public static void main(String[] args) {
            Scanner in = new Scanner(System.in);
            String a = in.next();
            char[] e = a.toCharArray();
            Stack<Character> s1 = new Stack<>();
            Stack<Integer> s2 = new Stack<>();
            int x1;
            int x2;
            for(int i=0;i<e.length;i++)
            {
                if(e[i] >= '0' && e[i] <= '9')
                {
                    int num;
                    num = e[i]-'0';
                    while(i<e.length-1)
                    {
                        if(!(e[i+1] >= '0' && e[i+1] <= '9'))
                        {
                            break;
                        }
                        
                        num *= 10;
                        num += (e[i+1] - '0');
                        i++;
                    }
                    s2.push(num);
                }
                else if(s1.isEmpty())
                {
                    s1.push(e[i]);
                }
                else if(e[i] == '(')
                {
                    s1.push(e[i]);
                }
                else if(e[i] == ')')
                {
                    char c3;
                    while(!s1.isEmpty() && (c3 = s1.pop()) != '(')
                    {
                        x2 = s2.pop();
                        x1 = s2.pop();
                        s2.push(calculate(x1,x2,c3));
                    }
                }
                else if(e[i] == '^')
                {
                    if(s1.peek() == '^')
                    {
                        char c3;
                        c3 = s1.pop();
                        x2 = s2.pop();
                        x1 = s2.pop();
                        s2.push(calculate(x1,x2,c3));
                    }
                    s1.push(e[i]);
                }
                else if(e[i] == '+' || e[i] == '-')
                {
                    if(s1.peek() != '(')
                    {
                        char c3;
                        while(!s1.isEmpty() && s1.peek() != '(')
                        {
                            c3 = s1.pop();
                            x2 = s2.pop();
                            x1 = s2.pop();
                            s2.push(calculate(x1,x2,c3));
                        }
                    }
                    s1.push(e[i]);
                }
                else
                {
                    char c3;
                    while(!(s1.peek() == '+' || s1.peek() == '-') && !s1.isEmpty() && s1.peek() != '(')
                    {
                        c3 = s1.pop();
                        x2 = s2.pop();
                        x1 = s2.pop();
                        s2.push(calculate(x1,x2,c3));
                    }
                    s1.push(e[i]);
                }
            }
            while(!s1.isEmpty())
            {
                char c3;
                c3 = s1.pop();
                x2 = s2.pop();
                x1 = s2.pop();
                s2.push(calculate(x1,x2,c3));
            }
            System.out.println(s2.pop());
            in.close();
        }
        public static int calculate(int x1,int x2,char c)
        {
            int sum = 0;
            switch (c)
            {
                case '+':sum = x1+x2;break;
                case '-':sum = x1-x2;break;
                case '*':sum = x1*x2;break;
                case '/':sum = x1/x2;break;
                case '^':sum = (int) Math.pow(x1,x2);break;
            }
            return sum;
        }
    }