Trie

关于Trie的几种实现方式

children node的存储

1可以用hashmap来存储children，HashMap<Character, TrieNode> children, 优势是利用contains函数便于查找

2用数组 TrieNode[] children; 通过index来查找，最多也就26个char(认为忽略大小写)

Search 函数：iterative 即可，可以将search和startwith合并

My solution ：HashMap + iterative

class TrieNode {
    // Initialize your data structure here.
    private char value;
    private boolean isend;// mark whether is end node
    
    //children of the node
    public HashMap<Character, TrieNode> children;
    
    public TrieNode() {
        isend = false;
        children = new HashMap<Character, TrieNode>();
    }
    public TrieNode(char c){
        value = c;
        isend = false;
        children = new HashMap<Character, TrieNode>();
    }
    public boolean isEnd(){
        return isend;
    }
    public void setEnd(){
        isend = true;
    }
}

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        if(word == null || word.length() == 0) return;
        //bfs level insert
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            HashMap<Character, TrieNode> child = cur.children;
            if(child.containsKey(c)){
                //no need insert
                cur = child.get(c);
            }else{
                //insert a new trie node
                TrieNode newchild = new TrieNode(c);
                child.put(c, newchild);
                cur = newchild;
            }
        }
        
        //mark end
        cur.setEnd();
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
       if(word == null || word.length() == 0) return false;
       TrieNode cur = root;
       for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            HashMap<Character, TrieNode> child = cur.children;
            if(!child.containsKey(c)){
                //no char 
                return false;
            }else{
                //continue search
                cur = child.get(c);
            }
        }
        return cur.isEnd();
       
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
       if(prefix == null || prefix.length() == 0) return false;
       TrieNode cur = root;
       
       for(int i = 0; i < prefix.length(); i++){
            char c = prefix.charAt(i);
            HashMap<Character, TrieNode> child = cur.children;
            if(!child.containsKey(c)){
                //no char 
                return false;
            }else{
                //continue search
                cur = child.get(c);
            }
        }
        return true;
    }
  
}

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

 

其他解法

class TrieNode {
    // Initialize your data structure here.
    private char value;
    private boolean isend;// mark whether is end node
    
    //children of the node
    public TrieNode[] children;
    
    public TrieNode() {
        isend = false;
        children = new TrieNode[26];
    }
    public TrieNode(char c){
        value = c;
        isend = false;
        children = new TrieNode[26];
    }
    public boolean isEnd(){
        return isend;
    }
    public void setEnd(){
        isend = true;
    }
}

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        if(word == null || word.length() == 0) return;
        //bfs level insert
        TrieNode cur = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            int index = c - 'a';
            if(cur.children[index] == null){
                //insert a new node
                cur.children[index] = new TrieNode(c);
            }
            cur = cur.children[index]; // go down
        }
        
        //mark end
        cur.setEnd();
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
       if(word == null || word.length() == 0) return false;
       TrieNode cur = root;
       
       for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            int index = c - 'a';
            if(cur.children[index] == null){
                //no such char
                return false;
            }
            cur = cur.children[index];
        }
        
        return cur.isEnd();
       
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
       if(prefix == null || prefix.length() == 0) return false;
       TrieNode cur = root;
       
       for(int i = 0; i < prefix.length(); i++){
            char c = prefix.charAt(i);
            int index = c - 'a';
            if(cur.children[index] == null){
                //no such char
                return false;
            }
            cur = cur.children[index];
        }
        return true;
    }
  
}