《个人软件开发流程》--杨瑞杰

 1 private static String[] op = { "+", "-", "*", "/" };
 2     /**
 3      * 生成算数表达式
 4      *
 5      * @return 运算表达式（无结果）
 6      */
 7     public static String MakeFormula() {
 8         StringBuilder build = new StringBuilder();
 9         // 生成区间范围[1,2],随机生成三位or四位的操作运算
10         int count = (int) (Math.random() * 2) + 1; // generate random count
11         int start = 0;
12         int number1 = (int) (Math.random() * 99) + 1;
13         build.append(number1);
14         while (start <= count) {
15             // 生成区间为[0,3]
16             int operation = (int) (Math.random() * 4); // generate operator（生成操作符）
17             int number2 = (int) (Math.random() * 99) + 1;
18             build.append(op[operation]).append(number2);
19             start++;
20         }
21         return build.toString();
22     }

 1 public static String Solve(String formula) {
 2         // stack堆栈
 3         Stack<String> tempStack = new Stack<>();// Store number or operator
 4         // Character表示基本类型 char 的 Class 实例。
 5         Stack<Character> operatorStack = new Stack<>();// Store operator
 6         int len = formula.length();
 7         int k = 0;
 8         for (int j = -1; j < len - 1; j++) {
 9             // charAt: 返回此序列中指定索引处的 char 值。
10             char formulaChar = formula.charAt(j + 1);
11             if (j == len - 2 || formulaChar == ‘+‘ || formulaChar == ‘-‘ || formulaChar == ‘/‘ || formulaChar == ‘*‘) {
12                 if (j == len - 2) {
13                     // subString:返回一个新的 String ，该子字符串始于指定索引处的字符，一直到此字符串末尾。
14                     tempStack.push(formula.substring(k));
15                 } else {
16                     if (k < j) {
17                         tempStack.push(formula.substring(k, j + 1));
18                     }
19                     // 判断是否为空
20                     if (operatorStack.empty()) {
21                         operatorStack.push(formulaChar); // if operatorStack is empty, store it
22                     } else {
23                         char stackChar = operatorStack.peek();
24                         if ((stackChar == ‘+‘ || stackChar == ‘-‘) && (formulaChar == ‘*‘ || formulaChar == ‘/‘)) {
25                             operatorStack.push(formulaChar);
26                         } else {
27                             tempStack.push(operatorStack.pop().toString());
28                             operatorStack.push(formulaChar);
29                         }
30                     }
31                 }
32                 k = j + 2;
33             }
34         }
35         while (!operatorStack.empty()) { // Append remaining operators
36             tempStack.push(operatorStack.pop().toString());
37         }
38         Stack<String> calcStack = new Stack<>();
39         for (String peekChar : tempStack) { // Reverse traversing of stack
40             if (!peekChar.equals("+") && !peekChar.equals("-") && !peekChar.equals("/") && !peekChar.equals("*")) {
41                 calcStack.push(peekChar); // Push number to stack
42             } else {
43                 int a1 = 0;
44                 int b1 = 0;
45                 if (!calcStack.empty()) {
46                     b1 = Integer.parseInt(calcStack.pop());
47                 }
48                 if (!calcStack.empty()) {
49                     a1 = Integer.parseInt(calcStack.pop());
50                 }
51                 switch (peekChar) {
52                 case "+":
53                     calcStack.push(String.valueOf(a1 + b1));
54                     break;
55                 case "-":
56                     calcStack.push(String.valueOf(a1 - b1));
57                     break;
58                 case "*":
59                     calcStack.push(String.valueOf(a1 * b1));
60                     break;
61                 default:
62                     calcStack.push(String.valueOf(a1 / b1));
63                     break;
64                 }
65             }
66         }
67         return formula + "=" + calcStack.pop();
68     }

 1 import java.util.Scanner;
 2 
 3 import org.junit.Test;
 4 
 5 import demo.demo1;
 6 
 7 public class TestCase {
 8     @Test
 9     public void test01() {
10         System.out.println("请输入表达式的个数：");
11         Scanner scanner = new Scanner(System.in);
12         int num = scanner.nextInt();
13         int i = 0;
14         while (i < num) {
15             String question = demo1.MakeFormula();
16             String ret = demo1.Solve(question);
17             System.out.println(ret);
18             i++;
19         }
20     }
21 
22 }