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 }