TrieTree

学习链接：https://blog.csdn.net/lisonglisonglisong/article/details/45584721

前缀树解决字符串前缀匹配问题，查找单词是否存在，统计以如“abc”开始的字符串的个数，实现词频统计等。

package class_07;

import java.util.HashMap;

public class Code_01_TrieTree {

	public static class TrieNode {
		public int path;   // 记录有多少个字符经过
		public int end;    // 记录有多少个字符串以此节点结尾
		public TrieNode[] nexts;  // 路
//		public HashMap<String, TrieNode> nexts;   也可以用HashMap来存储下一个节点
		public TrieNode() {
			path = 0;
			end = 0;
			nexts = new TrieNode[26];
		}
	}

	public static class Trie {
		private TrieNode root;

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

		public void insert(String word) {   
			if (word == null) {
				return;
			}
			char[] chs = word.toCharArray();
			TrieNode node = root;
			int index = 0;
			for (int i = 0; i < chs.length; i++) {
				index = chs[i] - 'a';
				if (node.nexts[index] == null) {  // 如果没有出现该字符对应的节点，创建
					node.nexts[index] = new TrieNode();
				}
				node = node.nexts[index];
				node.path++;             // 路径加一
			}
			node.end++;                  // 结尾的时候尾节点加一
		}

		public void delete(String word) {  //与 insert思路刚好相反
			if (search(word) != 0) {
				char[] chs = word.toCharArray();
				TrieNode node = root;
				int index = 0;
				for (int i = 0; i < chs.length; i++) {
					index = chs[i] - 'a';
					if (--node.nexts[index].path == 0) {
						node.nexts[index] = null;
						return;
					}
					node = node.nexts[index];
				}
				node.end--;
			}
		}

		public int search(String word) {
			if (word == null) {
				return 0;
			}
			char[] chs = word.toCharArray();
			TrieNode node = root;
			int index = 0;
			for (int i = 0; i < chs.length; i++) {
				index = chs[i] - 'a';
				if (node.nexts[index] == null) {
					return 0;
				}
				node = node.nexts[index];
			}
			return node.end;
		}

		public int prefixNumber(String pre) {    // 计算以pre为前缀的字符串个数
			if (pre == null) {
				return 0;
			}
			char[] chs = pre.toCharArray();
			TrieNode node = root;
			int index = 0;
			for (int i = 0; i < chs.length; i++) {
				index = chs[i] - 'a';
				if (node.nexts[index] == null) {
					return 0;
				}
				node = node.nexts[index];
			}
			return node.path;
		}
	}

	public static void main(String[] args) {
		Trie trie = new Trie();
		System.out.println(trie.search("zuo"));
		trie.insert("zuo");
		System.out.println(trie.search("zuo"));
		trie.delete("zuo");
		System.out.println(trie.search("zuo"));
		trie.insert("zuo");
		trie.insert("zuo");
		trie.delete("zuo");
		System.out.println(trie.search("zuo"));
		trie.delete("zuo");
		System.out.println(trie.search("zuo"));
		trie.insert("zuoa");
		trie.insert("zuoac");
		trie.insert("zuoab");
		trie.insert("zuoad");
		trie.delete("zuoa");
		System.out.println(trie.search("zuoa"));
		System.out.println(trie.prefixNumber("zuo"));

	}

}