[LeetCode] 208(LintCode). Implement Trie(Prefix Tree)

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

 Notice

You may assume that all inputs are consist of lowercase letters a-z.

 

Example

insert("lintcode")
search("code")
>>> false
startsWith("lint")
>>> true
startsWith("linterror")
>>> false
insert("linterror")
search("lintcode)
>>> true
startsWith("linterror")
>>> true

class Trie {
    class TrieNode{
        private char c;
        private Map<Character, TrieNode> map;
        private boolean isLeaf;   
        
        TrieNode() {
            this.map = new HashMap<>();
        }
        TrieNode(char c) {
            this.c = c;
            this.map = new HashMap<>();
        }
    }
    private TrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode currNode = root;
        for(int i = 0; i < word.length(); i++) {
            char currChar = word.charAt(i);
            if(!currNode.map.containsKey(currChar)) {
                TrieNode newNode = new TrieNode(currChar);    
                currNode.map.put(currChar, newNode);
                currNode = newNode;
            }
            else {
                currNode = currNode.map.get(currChar);
            }
            if(i == word.length() - 1) {
                currNode.isLeaf = true;
            }
        }
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode currNode = root;
        for(int i = 0; i < word.length(); i++) {
            if(!currNode.map.containsKey(word.charAt(i))) {
                return false;
            }
            currNode = currNode.map.get(word.charAt(i));
            if( i == word.length() - 1 && !currNode.isLeaf) {
                return false;
            }
        }
        return true;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode currNode = root;
        for(int i = 0; i < prefix.length(); i++) {
            if(!currNode.map.containsKey(prefix.charAt(i))) {
                return false;
            }
            currNode = currNode.map.get(prefix.charAt(i));
        }
        return true;        
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */