24点游戏

遍历法：

 1 public class Calculate {

 2 

 3     final double Threshold = 1E-6;

 4     final int CardsNumber = 4;

 5     final int ResultValue = 24;

 6     double number[] = new double[CardsNumber];

 7     String result[]=new String[CardsNumber];

 8     

 9     public boolean PointsGame(int n){

10         if(n == 1){

11             if(Math.abs(number[0]-ResultValue)<Threshold){

12                  System.out.println(result[0]);

13                  return true;

14             }else{

15                 return false;

16             }

17         }

18         for(int i=0; i<n ; i++){

19             for(int j=i+1; j<n; j++){

20                 double a,b;

21                 String expa, expb;

22                 a = number[i];

23                 b = number[j];

24                 number[j] = number[n - 1];

25                 

26                 expa = result[i];

27                 expb = result[j];

28                 result[j] = result[n - 1];

29                 

30                 result[i] = "(" + expa + "+" + expb + ")";

31                 number[i] = a + b;

32                 if(PointsGame(n - 1))

33                     return true;

34                 

35                 result[i] = "(" + expa + "-" + expb + ")";

36                 number[i] = a - b;

37                 if(PointsGame(n - 1))

38                     return true;

39                 

40                 result[i] = "(" + expb + "-" + expa + ")";

41                 number[i] = b - a;

42                 if(PointsGame(n - 1))

43                     return true;

44                 

45                 result[i] = "(" + expa + "*" + expb + ")";

46                 number[i] = a * b;

47                 if(PointsGame(n - 1))

48                     return true;

49                 

50                 if(b!=0){

51                     result[i] = "(" + expa + "/" + expb + ")";

52                     number[i] = a / b;

53                     if(PointsGame(n - 1))

54                         return true;

55                 }

56                 

57                 if(a!=0){

58                 result[i] = "(" + expb + "/" + expa + ")";

59                 number[i] = b - a;

60                 if(PointsGame(n - 1))

61                     return true;

62                 }

63                 

64                 number[i] = a;

65                 number[j] = b;

66                 result[i] = expa;

67                 result[j] = expb;

68             }

69         }

70         return false;

71     }

72     /**

73      * @param args

74      */

75     public static void main(String[] args) {

76 

77         Calculate ca = new Calculate();

78         ca.number[0] = 11;

79         ca.number[1] = 8;

80         ca.number[2] = 3;

81         ca.number[3] = 5;

82         ca.result[0] = "11";

83         ca.result[1] = "8";

84         ca.result[2] = "3";

85         ca.result[3] = "5";

86         ca.PointsGame(4);

87     }

88 

89 }