Trie树编程实现

Trie树

字典树，前缀树，单词查找树

应用：1)字符串检索 2）字符串最长公共前缀 3）英文单词的排序 4）作为其他数据结构和算法的辅助结构

结构图

    下面我们有and,as,at,cn,com这些关键词，那么如何构建trie树呢？下图是Trie的一种

节点存储内容：

1. 只存是不是单词的标识，用于对已知字符串匹配
2. 存储单个字母，用来查询或获取单词

特性

1. 根节点不包含字符，除根节点外的每一个子节点都包含一个字符或者标识
2. 从根节点到某一节点，路径上经过的字符连接起来，就是该节点对应的字符串（针对于节点存储内容的第2种情况，其余情况不一定）
3. 兄弟节点的前缀单词都相同

C++代码，节点只存储是否结束

#include 
#include 

using namespace std;


class TrieNode {
public:
	TrieNode* next[26];
	bool isWord;
	// Initialize your data structure here.
	TrieNode() :isWord{false} {
		memset(next, 0, sizeof(next));
	};
};

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

	// Inserts a word into the trie.
	void insert(string word) {
		TrieNode* p = root;
		int len = word.length();
		for (int i = 0; i < len; i++){
			char c = word[i];
			int index = c - 'a';
			if(p->next[index]==NULL)  p->next[index] = new TrieNode();
			p = p->next[index];
		}
		p->isWord = true;
	}

	// Returns if the word is in the trie.
	bool search(string word) {
		TrieNode* p = root;
		int len = word.length();
		for (int i = 0; i < len&&p; i++){
			p = p->next[word[i]-'a'];
		}
		return p&&p->isWord;
	}

	// Returns if there is any word in the trie
	// that starts with the given prefix.
	bool startsWith(string prefix) {
		TrieNode* p = root;
		int len = prefix.length();
		for (int i = 0; i < len&&p; i++){
			p = p->next[prefix[i] - 'a'];
		}
		return p;
	}

private:
	TrieNode* root;
};

// Your Trie object will be instantiated and called as such:
// Trie trie;
// trie.insert("somestring");
// trie.search("key");

Java代码，节点存储字母

class TrieNode {
    // Initialize your data structure here.
    char val;
    boolean isEnd=false;
    TrieNode[] children=new TrieNode[26];
    public TrieNode() {}
    public TrieNode(char val) {
        this.val=val;
    }
}

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode index=root;
        char[] words=word.toCharArray();
        for(int i=0,len=words.length;i<len;++i){
            if(index.children[words[i]-'a']!=null){
                index=index.children[words[i]-'a'];
            }else{
                TrieNode node=new TrieNode(words[i]);
                index.children[words[i]-'a']=node;
                index=node;
            }
            
        }
        index.isEnd=true;
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode index=root;
        char[] words=word.toCharArray();
        for(int i=0,len=words.length;i<len;++i){
            if(index.children[words[i]-'a']!=null){
                index=index.children[words[i]-'a'];
            }else{
                return false;
            }
        }
        
        return index.isEnd?true:false;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode index=root;
        char[] words=prefix.toCharArray();
        for(int i=0,len=words.length;i<len;++i){
            if(index.children[words[i]-'a']!=null){
                index=index.children[words[i]-'a'];
            }else{
                return false;
            }
        }
        

        return true;
    }
}