Longest Common Prefix

lcp.java

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.ArrayList;
import java.util.Iterator;

class Trie {
  
    private class TrieNode {
        Map<Character, TrieNode> children;
        boolean endOfWord;
        public TrieNode() {
            children = new HashMap<>();
            endOfWord = false;
        }
    }

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

    /**
     * Iterative implementation of insert into trie
     */
    public void insert(String word) {
        TrieNode current = root;
        for (int i = 0; i < word.length(); i++) {
            char ch = word.charAt(i);
            TrieNode node = current.children.get(ch);
            if (node == null) {
                node = new TrieNode();
                current.children.put(ch, node);
            } 
            current = node;
        }
        //mark the current nodes endOfWord as true
        current.endOfWord = true;
        
    }
    
    public void lcp() {
        
        StringBuilder prefix = new StringBuilder();
        TrieNode current = root;
        
        while(current != null && current.children.keySet().size() == 1 && !current.endOfWord){
            Set set = current.children.keySet();
            // the set will have only one key. We get that key.
            // then parse that key to char type and use that key to lookup in Hashmap
            String key = set.iterator().next().toString();
            TrieNode node = current.children.get(key.charAt(0));
            current = node;
            prefix.append(key.charAt(0));
        }
        
        System.out.println("LCP: " + prefix);
        
    }
    
    public static void main(String[] args) {
        
        Trie object = new Trie();
        object.insert("docag");
        object.insert("docdve");
        object.insert("docak");
        object.lcp();
    }
}