中缀表达式转成后缀表达式

参考

数据结构Java实现06----中缀表达式转换为后缀表达式

将中缀表达式转化为后缀表达式

 1 package collection_Exe;
 2
 3 import java.util.*;
 4
 5 public class Exe16 {
 6     public static void main(String[] args) {
 7         Scanner input = new Scanner(System.in);
 8         System.out.println("Input :");
 9         String string = input.nextLine();
10         input.close();
11         String[] strs = string.split(" ");
12         Set<String> set = new HashSet<>();
13         set.add("+");
14         set.add("-");
15         set.add("*");
16         set.add("/");
17         set.add("(");
18         set.add(")");
19         Stack<String> stack = new Stack<>();
20         Stack<String> operator = new Stack<>();
21         for(String str : strs) {
22             if(!set.contains(str)) {
23                 stack.push(str);
24             } else {
25                 switch (str) {
26                 case "+":
27                 case "-":
28                     if(!operator.isEmpty() &&
29                        !operator.peek().equals("(")) {
30                         stack.push(operator.pop());
31                     }
32                     operator.push(str);
33                     break;
34                 case "*":
35                 case "/":
36                     if(!operator.isEmpty() &&
37                        (operator.peek().equals("*") ||
38                          operator.peek().equals("/"))) {
39                         stack.push(operator.pop());
40                     }
41                     operator.push(str);
42                     break;
43                 case "(":
44                     operator.push(str);
45                     break;
46                 case ")":
47                     while (!operator.peek().equals("(")) {
48                         stack.push(operator.pop());
49                     }
50                     operator.pop();
51                     break;
52                 default:
53                     System.out.println("Error");
54                     break;
55                 }
56             }
57         }
58         while(!operator.isEmpty()) {
59             stack.push(operator.pop());
60         }
61         System.out.println(stack.toString());
62     }
63 }

你以为我会写注释吗？不可能的。

运行结果如下：

像我这种不拘小节的男人，是不会在意同优先级运算顺序的。

大概上，算法是没什么错误的。

 1 package collection_Exe;
 2
 3 import java.util.HashSet;
 4 import java.util.Scanner;
 5 import java.util.Set;
 6 import java.util.Stack;
 7
 8 public class Exe14 {
 9     public static void main(String[] args) {
10         Scanner input = new Scanner(System.in);
11         System.out.println("Input:");
12         String str = input.nextLine();
13         input.close();
14         String[] strs = proStr(str);
15         Stack<Integer> stack = new Stack<>();
16         Set<String> set = new HashSet<>();
17         set.add("+");
18         set.add("-");
19         set.add("*");
20         set.add("/");
21         for(String s : strs) {
22             if(set.contains(s)) {
23                 processStack(stack, s.charAt(0));
24             } else {
25                 stack.push(Integer.parseInt(s));
26             }
27         }
28         System.out.println("Result : " + stack.pop());
29     }
30
31     public static void processStack(Stack<Integer> stack, Character op) {
32         Integer num2 = stack.pop();
33         Integer num1 = stack.pop();
34         Integer num3 = null;
35         switch (op) {
36         case ‘+‘:
37             num3 = num1 + num2;
38             break;
39         case ‘-‘:
40             num3 = num1 - num2;
41             break;
42         case ‘*‘:
43             num3 = num1 * num2;
44             break;
45         case ‘/‘:
46             num3 = num1 / num2;
47             break;
48         default:
49             System.out.println("ERROR IN processStack.");
50             break;
51         }
52         stack.push(num3);
53     }
54
55     public static String[] proStr(String str) {
56         return str.split(" ");
57     }
58 }

自己凭本事写的bug。