Tries

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REF. geeksforgeeks

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class TrieNode {
    TrieNode[] children = new TrieNode[26];
    boolean isEndOfWord; // isEndOfWord is true if the node represents end of a word
}

class Trie {
    static TrieNode root=new TrieNode();
    // If not present, inserts key into trie
    // If the key is prefix of trie node,
    // just marks leaf node
    static void insert(String key) {
        int length = key.length();
        TrieNode p = root;

        for (int level = 0; level < length; level++) {
            int index = key.charAt(level) - 'a';
            if (p.children[index] == null){
                p.children[index] = new TrieNode();
            } 
            p = p.children[index];
        }
        // mark last node as leaf
        p.isEndOfWord = true;
    }

    // Returns true if key presents in trie, else false
    static boolean search(String key) {
        int length = key.length();
        TrieNode p = root;

        for (int level = 0; level < length; level++) {
            int index = key.charAt(level) - 'a';

            if (p.children[index] == null){
                return false;
            }
            
            p = p.children[index];
        }
        // if reach the key end and the node is the end of the word, return true.
        return (p != null && p.isEndOfWord);
    }
}

public class MyClass { // Driver
    public static void main(String args[]) {
        // Input keys (use only 'a' through 'z' and lower case)
        String keys[] = { "the", "a", "there", "answer", "any", "by", "bye", "their" };
        String output[] = { "Not present in trie", "Present in trie" };
        // Construct trie
        for (int i = 0; i < keys.length; i++)
            Trie.insert(keys[i]);

        // Search for different keys
        if (Trie.search("the") == true)
            System.out.println("the --- " + output[1]);
        else
            System.out.println("the --- " + output[0]);

        if (Trie.search("these") == true)
            System.out.println("these --- " + output[1]);
        else
            System.out.println("these --- " + output[0]);
        if (Trie.search("their") == true)
            System.out.println("their --- " + output[1]);
        else
            System.out.println("their --- " + output[0]);

        if (Trie.search("thaw") == true)
            System.out.println("thaw --- " + output[1]);
        else
            System.out.println("thaw --- " + output[0]);
    }
}


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