编译原理-逆波兰表达式JAVA算法

Demo

基于Java语言

[java] view plain copy

 

1. <span style="font-size:18px;">public class InversePoland {  
2.     // 9+(3-1)*3+10/2 = 20  
3.     //private static String[] ss = new String[]{"9","+","(","3","-","1",")","*","3","+","10","/","2"};  
4.        
5.     //24+3-8*(6-3)*2+10-3  
6.     private static String[] ss = new String[]{"24","+","3","-","8","*","(","6","-","3",")","*","2","+","10","-","3"};  
7.     private static Stack<String> stack = new Stack<String>();  
8.        
9.     //判断是否为数字  
10.     private boolean isNum(String s) {  
11.         if (s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/") || s.equals("(") || s.equals(")")) {  
12.             return false;  
13.         }  
14.         return true;  
15.     }  
16.        
17.     //获取符号优先级  
18.     private int getPriority(String s) {  
19.         if (s.equals("+") || s.equals("-")) {  
20.             return 1;  
21.         } else if (s.equals("*") || s.equals("/")) {  
22.             return 2;  
23.         }  
24.         return -1;  
25.     }  
26.        
27.     //输出字符串  
28.     private void print(String s) {  
29.         System.out.print(s + " ");  
30.     }  
31.        
32.     //符号操作  
33.     private void symbolOperation(String s) {  
34.         if (stack.size() == 0 || s.equals("(")) { //栈为空，直接进栈  
35.             stack.push(s);  
36.         } else if (s.equals(")")) {  //当前字符为“）”,则将栈中（以上的全部出栈输出  
37.             while (stack.size() > 0) {  
38.                 String pop_s = stack.pop();  
39.                 if(pop_s.equals("(")) {  
40.                     break;  
41.                 } else {  
42.                     print(pop_s);  
43.                 }  
44.             }   
45.         } else {  
46.             int pri_s = getPriority(s);  
47.             while (stack.size() > 0 ) {  
48.                 String top_s = stack.lastElement();  
49.                 if (top_s.equals("(")) {  
50.                     stack.push(s);  
51.                     return;  
52.                 } else {  
53.                     int top_pri = getPriority(top_s);  
54.                     if (pri_s <= top_pri) {  
55.                         String pop_s = stack.pop();  
56.                         print(pop_s);  
57.                     } else {  
58.                         break;  
59.                     }  
60.                 }  
61.             }  
62.             stack.push(s);  
63.         }  
64.     }  
65.        
66.     public void test() {  
67.         for (String s : ss) {  
68.             if (isNum(s)) {  
69.                 print(s);  
70.             } else {  
71.                 symbolOperation(s);  
72.             }  
73.         }  
74.         while (stack.size() > 0) {  
75.             String pop_s = stack.pop();  
76.             print(pop_s);  
77.         }  
78.     }  
79. }  
80. </span>  

输出结果

24 3 + 86 3 - * 2 * - 10 + 3 –