上海交通大学 计算表达式(java)

题目描述
对于一个不存在括号的表达式进行计算
输入描述:
存在多种数据，每组数据一行，表达式不存在空格
输出描述:
输出结果
示例1
输入
复制
6/2+3+3*4
输出
复制
18

import java.util.*;
import java.io.*;
import java.text.* ;
public class Main
{
	public static int[] pos = {0};
	public static char[] ch;
	public static HashMap<String, Integer> mon = new HashMap<>();
	public static int len;
	public static int i;
    public static void main(String[] args) throws ParseException{
    	try {
	        BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
	        ch = br.readLine().toCharArray();
	        System.out.println((int)compute());
 	    } catch (IOException e) {
	        e.printStackTrace();
	    }
    }
    public static double translation() {
    	double integer = 0.0;
    	double remainder = 0.0;
    	while(i < len && ch[i] >= '0' && ch[i] <= '9') {
    		integer *= 10;
    		integer += (ch[i] - '0');
    		i++;
    	}
    	if(i < len && ch[i] == '.') {
    		i++;
    		double c = 0.1;
        	while(ch[i] >= '0' && ch[i] <= '9') {
        		double t = ch[i] -'0';
        		t *= c;
        		c *= 0.1;
        		remainder += t;
        		i++;
        	}
    	}
    	return integer + remainder;
    }
    public static int getLevel(char ch)
    {
        switch (ch)
        {
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case '(':
            return 0;
        };
        return -1;
    }

	public static double operate(double a1, char op, double a2)
	{
	    switch (op)
	    {
	    case '+':
	        return a1 + a2;
	    case '-':
	        return a1 - a2;
	    case '*':
	        return a1 * a2;
	    case '/':
	        return a1 / a2;
	    };
	    return 0;
	}
	
	public static double compute() {
		Stack<Character> optr = new Stack<>();
		Stack<Double> opnd = new Stack<>();
		len = ch.length;
		boolean isMinus = true; // 判断'-'是减号还是负号, true表示负号
		for(i = 0; i < len;) {
			if(ch[i] == '-' && isMinus) {
				opnd.push(0.0);
				optr.push('-');
				i++;
			}
			else if(ch[i] == ')') {
				isMinus = false;
				i++;
				while(optr.peek() != '(') {
					double a2 = opnd.pop();
					double a1 = opnd.pop();
					char op = optr.pop();
					double result = operate(a1, op, a2);
					opnd.push(result);
				}
				optr.pop();
			}
			else if(ch[i] >= '0' && ch[i] <= '9') {
	            isMinus = false;
	            opnd.push(translation());
			}
			else if(ch[i] == '(') {
				isMinus = true;
				optr.push(ch[i]);
				i++;
			}
			else {
				while(!optr.empty() && getLevel(ch[i]) <= getLevel(optr.peek())) {
					double a2 = opnd.pop();
					double a1 = opnd.pop();
					char op = optr.pop();
					double result = operate(a1, op, a2);
					opnd.push(result);
				}
				optr.push(ch[i]);
				i++;
			}
		}
		while(!optr.empty()) {
			double a2 = opnd.pop();
			double a1 = opnd.pop();
			char op = optr.pop();
			double result = operate(a1, op, a2);
			opnd.push(result);			
		}
		return opnd.pop();
	}
}

附加：中缀转后缀

import java.util.*;
import java.io.*;
import java.text.* ;
public class Main
{
	public static int[] pos = {0};
	public static char[] ch;
	public static HashMap<String, Integer> mon = new HashMap<>();
	public static int len;
	public static int i;
	public static StringBuilder s;
    public static void main(String[] args) throws ParseException{
    	try {
	        BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
	        ch = br.readLine().toCharArray();
	        s = new StringBuilder();
	        compute();
	        System.out.println(s);
	        
 	    } catch (IOException e) {
	        e.printStackTrace();
	    }
    }
    public static String translation() {
    	StringBuilder tmp = new StringBuilder();
    	while(i < len && ch[i] >= '0' && ch[i] <= '9') {
    		tmp.append(ch[i]);
    		i++;
    	}
    	if(i < len && ch[i] == '.') {
    		tmp.append(ch[i]);
    		i++;
    		double c = 0.1;
        	while(ch[i] >= '0' && ch[i] <= '9') {
        		tmp.append(ch[i]);
        		i++;
        	}
    	}
    	return tmp.toString();
    }
    public static int getLevel(char ch)
    {
        switch (ch)
        {
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case '(':
            return 0;
        };
        return -1;
    }

	public static double operate(double a1, char op, double a2)
	{
	    switch (op)
	    {
	    case '+':
	        return a1 + a2;
	    case '-':
	        return a1 - a2;
	    case '*':
	        return a1 * a2;
	    case '/':
	        return a1 / a2;
	    };
	    return 0;
	}
	
	public static void compute() {
		Stack<Character> optr = new Stack<>();
		Stack<Double> opnd = new Stack<>();
		len = ch.length;
		boolean isMinus = true; // 判断'-'是减号还是负号, true表示负号
		for(i = 0; i < len;) {
			if(ch[i] == '-' && isMinus) {
				opnd.push(0.0);
				optr.push('-');
				i++;
			}
			else if(ch[i] == ')') {
				isMinus = false;
				i++;
				while(optr.peek() != '(') {
					char op = optr.pop();
					s.append(op);
				}
				optr.pop();
			}
			else if(ch[i] >= '0' && ch[i] <= '9') {
	            isMinus = false;
	            s.append(translation());
			}
			else if(ch[i] == '(') {
				isMinus = true;
				optr.push(ch[i]);
				i++;
			}
			else {
				while(!optr.empty() && getLevel(ch[i]) <= getLevel(optr.peek())) {
					char op = optr.pop();
					s.append(op);
				}
				optr.push(ch[i]);
				i++;
			}
		}
		while(!optr.empty()) {
			char op = optr.pop();
			s.append(op);			
		}
	}
}