傅老师课堂：TrieTree

        TrieTree与其说是一种算法，还不如说是一种解题的思路，我对海量数据的处理一直都是保持着一种积极的学习态度，TrieTree可以说是处理海量数据诸多方法中比较典型的一种，下面我提供了两种TrieTree的实现：使用动态数组和使用HashMap。

        1、动态数组的应用场景大多是使用在确定的较小范围的字符集，且字符的重复率较高。

        2、HashMap的应用场景大多是使用在较大范围的字符集，且字符的重复率不是很高。

Trie接口类：

package com.au.algorithm;import java.util.List;public interface Trie {public void add(String item);public List<String> getItemsWithPrefix(String prefix);public int getCount(String item);public List<String> getAllItems();public List<String> getMultiItems();public List<String> getSingleItems();}

使用HashMap实现的TrieTree：

package com.au.algorithm;import java.util.HashMap;import java.util.Iterator;import java.util.LinkedList;import java.util.List;import java.util.Map;/** *  * @author fuyouming *  */public class HashMapTrie implements Trie {private final Item root = new Item();/** * 字符节点的内部类 *  * @author fuyouming *  */private class Item {private int endCount = 0;// 多少个字符串以该字符做为结束符private Map<Integer, Item> nextItems = new HashMap<Integer, Item>();}public void add(String str) {add(root, str);}public List<String> getItemsWithPrefix(String prefix) {List<String> list = new LinkedList<String>();Item current = walk2FixedItem(prefix);if (current != null) {walk2NextItem(list, current, new StringBuffer(prefix));}return list;}public int getCount(String str) {Item current = walk2FixedItem(str);if (current != null) {return current.endCount;}return 0;}public List<String> getAllItems() {List<String> list = new LinkedList<String>();Iterator<Integer> iterator = root.nextItems.keySet().iterator();while (iterator.hasNext()) {Integer i = iterator.next();Item current = (Item) root.nextItems.get(i);StringBuffer buf = new StringBuffer().append((char) i.intValue());walk2NextItem(list, current, buf);}return list;}public List<String> getMultiItems() {return null;}public List<String> getSingleItems() {return null;}private void add(Item item, String str) {if (str.length() == 0) {item.endCount++;} else {int index = str.charAt(0);Item nextItem = null;if (!item.nextItems.containsKey(index)) {nextItem = new Item();item.nextItems.put(index, nextItem);} else {nextItem = (Item) item.nextItems.get(index);}add(nextItem, str.substring(1));}}private Item walk2FixedItem(String prefix) {if (prefix.length() > 0) {Item current = root;for (int i = 0; i < prefix.length(); i++) {int index = prefix.charAt(i);current = current.nextItems.get(index);if (current == null) {break;}}return current;} else {return null;}}private void walk2NextItem(List<String> list, Item previous,StringBuffer buf) {for (int i = 0; i < previous.endCount; i++) {list.add(buf.toString());}Iterator<Integer> iterator = previous.nextItems.keySet().iterator();while (iterator.hasNext()) {Integer i = iterator.next();Item current = (Item) previous.nextItems.get(i);StringBuffer newBuf = new StringBuffer(buf).append((char) i.intValue());walk2NextItem(list, current, newBuf);}}public static void main(String args[]) {Trie trie = new HashMapTrie();trie.add("ab");trie.add("abc");trie.add("abcd");trie.add("abd");trie.add("abd");trie.add("a cbd");trie.add("acrtfg");List<String> list = trie.getAllItems();for (String s : list) {System.out.println(s);}System.out.println("=================================");list = trie.getItemsWithPrefix("ac");for (String s : list) {System.out.println(s);}}}

使用动态数组实现的TrieTree：

package com.au.algorithm;import java.util.LinkedList;import java.util.List;/** *  * @author fuyouming *  */public class DynamicArrayTrie implements Trie {private final Item root = new Item();private int startASCII = 32;// 空格的ASCII码，排在它之前的字符都没有图形表示，所以不做处理private int endASCII = 255;// 最后一个字符的ASCII码/** * 字符节点的内部类 *  * @author fuyouming *  */private class Item {private int endCount = 0;// 多少个字符串以该字符做为结束符private Item[] nextItems = new Item[32];}public void add(String str) {add(root, str);}public List<String> getItemsWithPrefix(String prefix) {List<String> list = new LinkedList<String>();Item current = walk2FixedItem(prefix);if (current != null) {walk2NextItem(list, current, new StringBuffer(prefix));}return list;}public int getCount(String str) {Item current = walk2FixedItem(str);if (current != null) {return current.endCount;}return 0;}public List<String> getAllItems() {List<String> list = new LinkedList<String>();for (int i = 0; i < root.nextItems.length; i++) {Item current = root.nextItems[i];if (current != null) {StringBuffer buf = new StringBuffer().append(idx2Chr(i));walk2NextItem(list, current, buf);}}return list;}public List<String> getMultiItems() {return null;}public List<String> getSingleItems() {return null;}private void add(Item item, String str) {if (str.length() == 0) {item.endCount++;} else {int index = chr2Idx(str.charAt(0));ensureCapacity(item, index);if (item.nextItems[index] == null) {item.nextItems[index] = new Item();}add(item.nextItems[index], str.substring(1));}}private int chr2Idx(char c) {return c - startASCII;}private char idx2Chr(int i) {return (char) (i + startASCII);}private void ensureCapacity(Item item, int index) {if (index + 1 > item.nextItems.length) {Item[] oldItems = item.nextItems;item.nextItems = new Item[Math.min(endASCII - startASCII,oldItems.length + Math.max(10, index - oldItems.length)) + 1];System.arraycopy(oldItems, 0, item.nextItems, 0, oldItems.length);}}private Item walk2FixedItem(String prefix) {if (prefix.length() > 0) {Item current = root;for (int i = 0; i < prefix.length(); i++) {int index = chr2Idx(prefix.charAt(i));current = current.nextItems[index];if (current == null) {break;}}return current;} else {return null;}}private void walk2NextItem(List<String> list, Item previous,StringBuffer buf) {for (int i = 0; i < previous.endCount; i++) {list.add(buf.toString());}for (int i = 0; i < previous.nextItems.length; i++) {Item current = previous.nextItems[i];if (current != null) {StringBuffer newBuf = new StringBuffer(buf).append(idx2Chr(i));walk2NextItem(list, current, newBuf);}}}public static void main(String args[]) {Trie trie = new DynamicArrayTrie();trie.add("ab");trie.add("abc");trie.add("abcd");trie.add("abd");trie.add("abd");trie.add("a cbd");trie.add("acrtfg");List<String> list = trie.getAllItems();for (String s : list) {System.out.println(s);}System.out.println("=================================");list = trie.getItemsWithPrefix("ac");for (String s : list) {System.out.println(s);}}}