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; } }}}