public class TrieNode {

 public TrieNode[] children;

 public char data;

 public int freq;

 public TrieNode() {
 //因为有26个字母
 children = new TrieNode[26];
 freq = 0;
 }

}

public class TrieTree {

 private TrieNode root;

 public TrieTree(){
 root=new TrieNode();
 }

 ...

}

 public void insert(String word){
 if(TextUtils.isEmpty(word)){
  return;
 }
 insertNode(root,word.toCharArray(),0);
 }

 private static void insertNode(TrieNode rootNode,char[]charArray,int index){

 int k=charArray[index]-'a';
 if(k<0||k>25){
  throw new RuntimeException("charArray[index] is not a alphabet!");
 }
 if(rootNode.children[k]==null){
  rootNode.children[k]=new TrieNode();
  rootNode.children[k].data=charArray[index];
 }

 if(index==charArray.length-1){
  rootNode.children[k].freq++;
  return;
 }else{
  insertNode(rootNode.children[k],charArray,index+1);
 }

 }

 public void remove(String word){
 if(TextUtils.isEmpty(word)){
  return;
 }
 remove(root,word.toCharArray(),0);
 }

 private static void remove(TrieNode rootNode,char[]charArray,int index){
 int k=charArray[index]-'a';
 if(k<0||k>25){
  throw new RuntimeException("charArray[index] is not a alphabet!");
 }
 if(rootNode.children[k]==null){
  //it means we cannot find the word in this tree
  return;
 }

 if(index==charArray.length-1&&rootNode.children[k].freq >0){
  rootNode.children[k].freq--;
 }

 remove(rootNode.children[k],charArray,index+1);
 }

 public int getFreq(String word){
 if(TextUtils.isEmpty(word)){
  return 0;
 }
 return getFreq(root,word.toCharArray(),0);
 }

 private static int getFreq(TrieNode rootNode,char[]charArray,int index){
 int k=charArray[index]-'a';
  if(k<0||k>25){
  throw new RuntimeException("charArray[index] is not a alphabet!");
 }
 //it means the word is not in the tree
 if(rootNode.children[k]==null){
  return 0;
 }
 if(index==charArray.length-1){
  return rootNode.children[k].freq;
 }
 return getFreq(rootNode.children[k],charArray,index+1);
 }

 public static void test(){
 TrieTree trieTree=new TrieTree();
 String sourceStr="Democratic presumptive nominee Hillary Clintons campaign posed pounced on Trumps assertion that British term monetary turmoil might benefit his business venture in Scotland";

 //String sourceStr="the that";
 sourceStr=sourceStr.toLowerCase();

 String[]strArray=sourceStr.split(" ");
 for(String str:strArray){
  trieTree.insert(str);
 }


 String sourceStr2="Every president is tested by world events But Donald Trump thinks about how is his golf resort can profit from that";
 sourceStr2=sourceStr2.toLowerCase();
 String[]strArray2=sourceStr2.split(" ");
 for(String str:strArray2){
  trieTree.insert(str);
 }



 BinaryTree.print("frequence of 'that':"+trieTree.getFreq("that"));
 BinaryTree.print("\nfrequence of 'donald':"+trieTree.getFreq("donald"));

 trieTree.remove("that");
 BinaryTree.print("\nafter remove 'that' once,freq of 'that':"+trieTree.getFreq("that"));
 trieTree.remove("that");
 BinaryTree.print("\nafter remove 'that' twice,freq of 'that':"+trieTree.getFreq("that"));

 trieTree.remove("donald");
 BinaryTree.print("\nafter remove 'donald' once,freq of 'donald':"+trieTree.getFreq("donald"));

 BinaryTree.reallyStartPrint();


 }