LeetCode – Add and Search Word – Data structure design (Java)

Category: Algorithms >> Interview >> Java May 16, 2014

Design a data structure that supports the following two operations:

void addWord(word)
bool search(word)

search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.

Java Solution 1

This problem is similar with Implement Trie. The solution 1 below uses the same definition of a trie node. To handle the "." case for this problem, we need to search all possible paths, instead of one path.

TrieNode

class TrieNode{
    char c;
    HashMap<Character, TrieNode> children = new HashMap<Character, TrieNode>();
    boolean isLeaf;
 
    public TrieNode() {}
 
    public TrieNode(char c){
        this.c = c;
    }
}

WordDictionary

public class WordDictionary {
    private TrieNode root;
 
    public WordDictionary(){
        root = new TrieNode();
    }
 
    // Adds a word into the data structure.
    public void addWord(String word) {
        HashMap<Character, TrieNode> children = root.children;
 
        for(int i=0; i<word.length(); i++){
            char c = word.charAt(i);
 
            TrieNode t = null;
            if(children.containsKey(c)){
                t = children.get(c);
            }else{
                t = new TrieNode(c);
                children.put(c,t);
            }
 
            children = t.children;
 
            if(i == word.length()-1){
                t.isLeaf = true;
            }
        }
    }
 
    // Returns if the word is in the data structure. A word could
    // contain the dot character '.' to represent any one letter.
    public boolean search(String word) {
       return dfsSearch(root.children, word, 0);
 
    }
 
     public boolean dfsSearch(HashMap<Character, TrieNode> children, String word, int start) {
        if(start == word.length()){
            if(children.size()==0) 
                return true; 
            else
                return false;
        }
 
        char c = word.charAt(start);    
 
        if(children.containsKey(c)){
            if(start == word.length()-1 && children.get(c).isLeaf){
                return true;
            }
 
            return dfsSearch(children.get(c).children, word, start+1);
        }else if(c == '.'){
            boolean result = false;
            for(Map.Entry<Character, TrieNode> child: children.entrySet()){
                if(start == word.length()-1 && child.getValue().isLeaf){
                    return true;
                } 
 
                //if any path is true, set result to be true; 
                if(dfsSearch(child.getValue().children, word, start+1)){
                    result = true;
                }
            }
 
            return result;
        }else{
            return false;
        }
    }
}

Java Solution 2 - Using Array Instead of HashMap

class TrieNode{
    TrieNode[] arr;
    boolean isLeaf;
 
    public TrieNode(){
        arr = new TrieNode[26];
    }    
}
 
public class WordDictionary {
    TrieNode root;
 
    public WordDictionary(){
        root = new TrieNode();
    }
    // Adds a word into the data structure.
    public void addWord(String word) {
        TrieNode p= root;
        for(int i=0; i<word.length(); i++){
            char c=word.charAt(i);
            int index = c-'a';
            if(p.arr[index]==null){
                TrieNode temp = new TrieNode();
                p.arr[index]=temp;
                p=temp;
            }else{
                p=p.arr[index];
            }
        }
 
        p.isLeaf=true;
    }
 
    // Returns if the word is in the data structure. A word could
    // contain the dot character '.' to represent any one letter.
    public boolean search(String word) {
        return dfsSearch(root, word, 0);     
    }
 
   public boolean dfsSearch(TrieNode p, String word, int start) {
		if (p.isLeaf && start == word.length())
			return true;
 
		if (start >= word.length())
			return false;
 
		char c = word.charAt(start);
 
		if (c == '.') {
			boolean tResult = false;
			for (int j = 0; j < 26; j++) {
				if (p.arr[j] != null) {
					if (dfsSearch(p.arr[j], word, start + 1)) {
						tResult = true;
						break;
					}
				}
			}
 
			if (tResult)
				return true;
		} else {
			int index = c - 'a';
 
			if (p.arr[index] != null) {
				return dfsSearch(p.arr[index], word, start + 1);
			} else {
				return false;
			}
		}
 
		return false;
	}
}

Category >> Algorithms >> Interview >> Java

If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:

<pre><code> 
String foo = "bar";
</code></pre>

NightCoder

Can anyone tell me why this fails on Leetcode 7th test cases

class WordDictionary { class TrieNode { Map children; Boolean endOfWord; public TrieNode() { this.children = new HashMap(); this.endOfWord = false; } } TrieNode root = new TrieNode(); /** Adds a word into the data structure. */ public void addWord(String word) { if(word == null) return ; TrieNode curr = root; for(int i = 0; i < word.length(); i++){ char c = word.charAt(i); TrieNode trie = curr.children.get(c); if(trie == null){ trie = new TrieNode(); curr.children.put(c,trie); } curr = trie; } curr.endOfWord = true; } /** Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter. */ public boolean search(String word) { TrieNode curr = root; LinkedList queue = new LinkedList(); queue.add(curr); int level = 0; int len = word.length() - 1; while (!queue.isEmpty() && level <= len) { char c = word.charAt(level); int size = queue.size(); for (int i = 0; i < size; i++) { Map children = queue.remove().children; TrieNode temp = children.get(c); if (temp != null) { if (level == len && temp.endOfWord) return true; queue.add(temp); } else if (c == '.') { for(Map.Entry entry : children.entrySet()){ queue.add(entry.getValue()); } } else return false; } level++; } return true; } }
Weiran Liu

You can pass the TLE by setting special case for search(“.”)
Just check if root has only one child node
Suzy

Time out as well. 🙁
spoiledPiggy

Did you pass the OJ? TLE here.

LeetCode – Add and Search Word – Data structure design (Java)

Related posts: