计算后缀表达式

喜欢ヅ旅行 2022-06-13 05:22 163阅读 0赞

package stack;
    
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.util.Stack;
    /*
     * 计算后缀表达式的值
     * 如下6,5,2,3,+,8,*,+,3,+,*
     *    2,1,+,4,*
     *    4,13,5,/,+,10,*
     */
    public class Test {
    
    	public static void main(String[] args) {
    		System.out.println("请输入后缀表达式(字符间以英文逗号隔开)：");
    		BufferedReader reader=new BufferedReader(new InputStreamReader(System.in));
    		String str=null;
    		try {
    			str=reader.readLine();
    		} catch (IOException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		String[] ss=str.split(",");
    		postfixExpression(ss);
    	}
    	
    	public static void postfixExpression(String[] ss){
    		int value=0;//计算值
    		StringBuilder sb=new StringBuilder();//保存表达式
    		boolean flag=false;
    //		String[] ss={"2","1","+","4","*"};  
    //		String[] ss={"4","13","5","/","+","10","*"};
    		Stack<String> newStack=new Stack<String>();//用栈来保存表达式元素
    		for(String s:ss){
                if(validate(s)){//是否是运算符
                	String s1=newStack.pop();//是的话出栈两个元素
                	String s2=newStack.pop();          		
                	value=operator(s1, s2, s);//两位数运算
                	if(sb.length()>0){
                		//取最后一位字符，判断是否是）
                		String lastSb=sb.substring(sb.length()-1);	
                		if(lastSb.equals(")")){
                			if(flag){//判断计算后代值入栈是栈内是否还有元素
                				sb.insert(0, "("+s2+s);//加到字符串开头
                				sb.append(")");
                			}else{		
                				sb.insert(0, "(");
                				sb.append(s+s1+")");//加到末尾
                			}
                			flag=false;
                		}else{
                			sb.append("("+s2+s+s1+")");
                		}
                	}else{
            			sb.append("("+s2+s+s1+")");
            		}
                	if(newStack.size()>0){
                		flag=true;
                	}
                	newStack.push(String.valueOf(value));
                }else{
                	newStack.push(s);
                }	
    		}
    		System.out.println(sb.toString()+"="+value);
    	}
    	
    	public static boolean validate(String s){
    		boolean flag=false;
    		if(s.equals("+")){
    			flag=true;
    		}else if(s.equals("-")){
    			flag=true;
    		}else if(s.equals("*")){
    			flag=true;
    		}else if(s.equals("/")){
    			flag=true;
    		}
    		return flag;
    	}
    	
        public static int operator(String s1,String s2,String operator){
        	int num=0;
        	int num1=Integer.valueOf(s1);
    		int num2=Integer.valueOf(s2);
    		switch(operator){
    		   case "+":
    			   num=num2+num1;
    			   break;
    		   case "*":
    			   num=num2*num1;
    			   break;
    		   case "-":
    			   num=num2-num1;
    			   break;
    		   case "/":
    			   num=num2/num1;
    			   break;
    		}
        	return num;
        }
    }

[http://blog.csdn.net/xdkb159/article/details/73848939][http_blog.csdn.net_xdkb159_article_details_73848939]

[http_blog.csdn.net_xdkb159_article_details_73848939]: http://blog.csdn.net/xdkb159/article/details/73848939