Create Trie.java

Trie.java

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+public class Trie {
+
+    // Alphabet size (# of symbols)
+    static final int ALPHABET_SIZE = 26;
+
+    // trie node
+    static class TrieNode
+    {
+        TrieNode[] children = new TrieNode[ALPHABET_SIZE];
+
+        // isEndOfWord is true if the node represents
+        // end of a word
+        boolean isEndOfWord;
+
+        TrieNode(){
+            isEndOfWord = false;
+            for (int i = 0; i < ALPHABET_SIZE; i++)
+                children[i] = null;
+        }
+    };
+
+    static TrieNode root;
+
+    // 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 level;
+        int length = key.length();
+        int index;
+
+        TrieNode pCrawl = root;
+
+        for (level = 0; level < length; level++)
+        {
+            index = key.charAt(level) - 'a';
+            if (pCrawl.children[index] == null)
+                pCrawl.children[index] = new TrieNode();
+
+            pCrawl = pCrawl.children[index];
+        }
+
+        // mark last node as leaf
+        pCrawl.isEndOfWord = true;
+    }
+
+    // Returns true if key presents in trie, else false
+    static boolean search(String key)
+    {
+        int level;
+        int length = key.length();
+        int index;
+        TrieNode pCrawl = root;
+
+        for (level = 0; level < length; level++)
+        {
+            index = key.charAt(level) - 'a';
+
+            if (pCrawl.children[index] == null)
+                return false;
+
+            pCrawl = pCrawl.children[index];
+        }
+
+        return (pCrawl.isEndOfWord);
+    }
+
+    // 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"};
+
+
+        root = new TrieNode();
+
+        // Construct trie
+        int i;
+        for (i = 0; i < keys.length ; i++)
+            insert(keys[i]);
+
+        // Search for different keys
+        if(search("the") == true)
+            System.out.println("the --- " + output[1]);
+        else System.out.println("the --- " + output[0]);
+
+        if(search("these") == true)
+            System.out.println("these --- " + output[1]);
+        else System.out.println("these --- " + output[0]);
+
+        if(search("their") == true)
+            System.out.println("their --- " + output[1]);
+        else System.out.println("their --- " + output[0]);
+
+        if(search("thaw") == true)
+            System.out.println("thaw --- " + output[1]);
+        else System.out.println("thaw --- " + output[0]);
+
+    }
+}