java字符串排列和组合查找

// Gets all the permutations of a string.
void permuteString(String beginningString,String endingString) {
    if (endingString.length() <= 1){
        if((Arrays.binarySearch(mDictionary,beginningString.toLowerCase() +   endingString.toLowerCase())) >= 0){
            mWordSet.add(beginningString + endingString);
        }
    }
    else
        for (int i = 0; i < endingString.length(); i++) {
            String newString = endingString.substring(0,i) + endingString.substring(i + 1);
            permuteString(beginningString + endingString.charAt(i),newString);
      }
}
// Get the combinations of the sub-strings. Minimum 3 letter combinations
void subStrings(String s){
    String newString = "";
    if(s.length() > 3){
        for(int x = 0; x < s.length(); x++){
            newString = removeCharAt(x,s);
            permuteString("",newString);
            subStrings(newString);
        }
    }
}

上面的代码运行正常,但是当我将其安装在我的Nexus上时,我意识到它运行有点太慢了.完成需要几秒钟.大概3或4秒是不能接受的.
现在我已经在手机上玩过一些文字游戏,他们会立即计算一个字符串的所有组合,这使我相信我的算法效率不高,可以改进.谁能帮忙？

public class TrieNode {
TrieNode a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z;
TrieNode[] children = {a,z};
private ArrayList<String> words = new ArrayList<String>();

public void addWord(String word){
    words.add(word);
}
public ArrayList<String> getWords(){
    return words;
}
}

public class Trie {

static String myWord;
static String myLetters = "afinnrty";
static char[] myChars;
static Sort sort;
static TrieNode myNode = new TrieNode();
static TrieNode currentNode;
static int y = 0;
static ArrayList<String> availableWords = new ArrayList<String>();

public static void main(String[] args) {

    readWords();
    getPermutations();
}
public static void getPermutations(){
    currentNode = myNode;
    for(int x = 0; x < myLetters.length(); x++){
        if(currentNode.children[myLetters.charAt(x) - 'a'] != null){
            //availableWords.addAll(currentNode.getWords());
            currentNode = currentNode.children[myLetters.charAt(x) - 'a'];
            System.out.println(currentNode.getWords() + "" + myLetters.charAt(x));
        }
    }
    //System.out.println(availableWords);
}
public static void readWords(){
    try {
        BufferedReader in = new BufferedReader(new FileReader("c://scrabbledictionary.txt"));
        String str;
        while ((str = in.readLine()) != null) {
            myWord = str;
            myChars = str.toCharArray();
            sort = new Sort(myChars);
            insert(myNode,myChars,0);
        }
        in.close();
    } catch (IOException e) {
    }
}
public static void insert(TrieNode node,char[] myChars,int x){    
    if(x >= myChars.length){
        node.addWord(myWord);
        //System.out.println(node.getWords()+""+y);
        y++;
        return;
    }
    if(node.children[myChars[x]-'a'] == null){
        insert(node.children[myChars[x]-'a'] = new TrieNode(),x=x+1);
    }else{
        insert(node.children[myChars[x]-'a'],x=x+1);
    }
}
}