分治思想找24

原文:
[url]
http://hi.baidu.com/cesul/blog/item/998796880ba02899a5c2720b.html
[/url]

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class Find24 {
private static double threshold = 1E-6;
private static Double [] number = new Double[4];
private static String [] result = new String[4];
static Set<String> set = new HashSet<String>();

public static void main(String[] args) throws Exception{
   //获取输入
   System.out.println("请输入数字：（输入一个空一行）");
   BufferedReader bf;
   for (int i = 0; i < 4; i++) {
    bf = new BufferedReader(new InputStreamReader(System.in));
    result[i] = bf.readLine();
    number[i] = Double.valueOf(result[i]);
   }
   System.out.println("你输入的数字是：" + result[0]+ ", " + result[1]+ ", " + result[2]+ ", " + result[3]);
  
   Recurse_find(4);
  
   //用一个去除重复的HashSet统计结果并输出
   Iterator<String> it=set.iterator();
   while(it.hasNext()){
    System.out.println(it.next());
   }
   System.out.println("共有" + set.size() + "条参考结果。"); 
  
}

private static void Recurse_find(int n) {
   if (n == 1) {
    if( Math.abs(number[0] - 24) < threshold ){
     set.add(result[0].substring(1, result[0].length()-1) + " = 24"); //符合加入HashSet
    }else{
    }
   }
  
   for (int i = 0; i < n; i++) 
   {
    for (int j = i+1; j < n; j++) 
    {
    	
     double a, b; 
     String expa, expb;
     a = number[i];
     b = number[j];
     number[j] = number[n-1];
    
     expa = result[i];
     expb = result[j];
     result[j] = result[n-1];
    
     result[i] = "(" + expa + "+" + expb + ")";
     number[i] = a+b;
     Recurse_find(n-1);
    
     result[i] = "(" + expa + "-" + expb + ")";
     number[i] = a-b;
     Recurse_find(n-1);

     result[i] = "(" + expb + "-" + expa + ")";
     number[i] = b-a;
     Recurse_find(n-1);
  
     result[i] = "(" + expa + "*" + expb + ")";
     number[i] = a*b;
     Recurse_find(n-1);
    
     if(b != 0){
      result[i] = "(" + expa + "/" + expb + ")";
      number[i] = a/b;
      Recurse_find(n-1); 
     }
    
     if (a != 0) {
      result[i] = "(" + expb + "/" + expa + ")";
      number[i] = b/a;
      Recurse_find(n-1); 
     }
    
     number[i] = a;
     number[j] = b;
     result[i] = expa;
     result[j] = expb;
    }
   }
}
}