字符串所有可能的排列 例如abcd等等 递归算法和排列组合知识结合

可以用在md5编码等

package test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.eetrust.raf.core.utils.encrypt.SecureMD5;

/**
*
* @author chenhui
*
*/
public class Test2 {

private StringBuilder builder = null;
private static String KEY = "abcdef";
private static String DBPWD = "AzoAMg9rWj";

/**
* @param str
* 字符串str中每个字符都不相同
* @return 字符串str所有可能的排列
*/
public List<String> doCompute(String str) {
List<String> list = new ArrayList<String>();
List<String> temp = null;
if (str.length() == 1) {
list.add(str);
return list;
} else {
char ch = str.charAt(0);
temp = doCompute(str.substring(1));
for (int j = 0; j < temp.size(); j++) {
String s = temp.get(j);
builder = new StringBuilder(s.length() + 1);
// 将ch分别放到s.length() + 1个位置
for (int k = 0; k < s.length() + 1; k++) {
builder.append(s.substring(0, k));
builder.append(ch);
builder.append(s.substring(k, s.length()));
list.add(j, builder.toString());
builder.delete(0, s.length() + 1);
}
}
for (int i = 0; i < temp.size(); i++) {
temp.remove(i);
}
temp = null;
return list;
}
}

private static boolean vString(String str){
//System.out.println("验证过：" + str);
return SecureMD5.passDecrypt(DBPWD,KEY).equals(str);
}

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub

Test2 abc = new Test2();
long t1 = System.currentTimeMillis();
List<String> list = abc.doCompute("89123");
long t2 = System.currentTimeMillis();
Collections.sort(list);
long t3 = System.currentTimeMillis();
for (String s : list) {
if (vString(s)) {
System.out.println("::" + s);
return;
}
}
System.out.println(t2 - t1);
System.out.println(t3 - t2);
}
}