lintcode-medium-Implement Trie

Implement a trie with insert, search, and startsWith methods.

 

/**
 * Your Trie object will be instantiated and called as such:
 * Trie trie = new Trie();
 * trie.insert("lintcode");
 * trie.search("lint"); will return false
 * trie.startsWith("lint"); will return true
 */
class TrieNode {
    // Initialize your data structure here.
    char c;
    HashMap<Character, TrieNode> children;
    boolean isLeaf;
    
    public TrieNode() {
        this.children = new HashMap<Character, TrieNode>();
        this.isLeaf = false;
    }
    
    public TrieNode(char c){
        this.c = c;
        this.children = new HashMap<Character, TrieNode>();
        this.isLeaf = false;
    }
    
}

public class Solution {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        if(word == null || word.length() == 0)
            return;
        
        TrieNode temp = root;
        
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            
            if(temp.children.containsKey(c)){
                temp = temp.children.get(c);
            }
            else{
                temp.children.put(c, new TrieNode(c));
                temp = temp.children.get(c);
            }
            
            if(i == word.length() - 1)
                temp.isLeaf = true;
        }
        
        return;
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        if(word == null || word.length() == 0)
            return true;
        
        TrieNode temp = root;
        
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            
            if(temp.children.containsKey(c)){
                temp = temp.children.get(c);
            }
            else
                return false;
            
        }
        
        return temp.isLeaf;
    }

    // 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 true;
        
        TrieNode temp = root;
        
        for(int i = 0; i < prefix.length(); i++){
            char c = prefix.charAt(i);
            
            if(temp.children.containsKey(c)){
                temp = temp.children.get(c);
            }
            else
                return false;
            
        }
        
        return true;
    }
}