Getting a list of words from a Trie

Question

I\'m looking to use the following code to not check whether there is a word matching in the Trie but to return a list all words beginning with the prefix inputted by the use

Answer 1

I faced this problem while trying to make a text auto-complete module. I solved the problem by making a Trie in which each node contains it's parent node as well as children. First I searched for the node starting at the input prefix. Then I applied a Traversal on the Trie that explores all the nodes of the sub-tree with it's root as the prefix node. whenever a leaf node is encountered, it means that the end of a word starting from input prefix has been found. Starting from that leaf node I iterate through the parent nodes getting parent of parent, and reach the root of the subtree. While doing so I kept adding the keys of nodes in a stack. In the end I took the prefix and started appended it by popping the stack. I kept on saving the words in an ArrayList. At the end of the traversal I get all the words starting from the input prefix. Here is the code with usage example:

class TrieNode
{
    char c;
    TrieNode parent;
    HashMap children = new HashMap();
    boolean isLeaf;

    public TrieNode() {}
    public TrieNode(char c){this.c = c;}
}

-

public class Trie
{
    private TrieNode root;
    ArrayList words; 
    TrieNode prefixRoot;
    String curPrefix;

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

    // Inserts a word into the trie.
    public void insert(String word) 
    {
        HashMap children = root.children;

        TrieNode crntparent;

        crntparent = root;

        //cur children parent = root

        for(int i=0; i children = root.children; 
        TrieNode t = null;
        for(int i=0; i hstack = new Stack(); 

          while(altair != prefixRoot)
          {
            //println(altair.c);
            hstack.push( Character.toString(altair.c) );
            altair = altair.parent;
          }

          String wrd = curPrefix;

          while(hstack.empty()==false)
          {
            wrd = wrd + hstack.pop();
          }

          //println(wrd);
          words.add(wrd);

        }

         Set kset = node.children.keySet();
         //println(node.c); println(node.isLeaf);println(kset);
         Iterator itr = kset.iterator();
         ArrayList aloc = new ArrayList();

       while(itr.hasNext())
       {
        Character ch = (Character)itr.next();  
        aloc.add(ch);
        //println(ch);
       } 

     // here you can play with the order of the children

       for( int i=0;i

Example

Trie prefixTree;

prefixTree = new Trie();  

  prefixTree.insert("GOING");
  prefixTree.insert("GONG");
  prefixTree.insert("PAKISTAN");
  prefixTree.insert("SHANGHAI");
  prefixTree.insert("GONDAL");
  prefixTree.insert("GODAY");
  prefixTree.insert("GODZILLA");

  if( prefixTree.startsWith("GO")==true)
  {
    TrieNode tn = prefixTree.searchNode("GO");
    prefixTree.wordsFinderTraversal(tn,0);
    prefixTree.displayFoundWords(); 

  }

  if( prefixTree.startsWith("GOD")==true)
  {
    TrieNode tn = prefixTree.searchNode("GOD");
    prefixTree.wordsFinderTraversal(tn,0);
    prefixTree.displayFoundWords(); 

  }