Added code for no prefix set problem

NoPrefixSet.java

@@ -0,0 +1,91 @@
+import java.io.*;
+import java.util.*;
+
+public class Trie {
+
+    private static final int ALPHABET_SIZE = 26;
+
+	class Node {
+
+	    Node[] edges;
+	    char key;
+	    int wordCount = 0;
+	    int prefixCount = 0;
+
+	    Node(char key) {
+	        this.key = key;
+	        this.edges = new Node[ALPHABET_SIZE];
+	    }
+
+	    boolean has(char key) {
+	        return get(key) != null;
+	    }
+
+	    Node get(char key) {
+    	    return edges[getKey(key)];
+	    }
+
+	    void put(char key, Node node) {
+	        this.edges[getKey(key)] = node;
+	    }
+
+	    char getKey(char ch) {
+	        return (char) (ch - 'a');
+	    }
+
+	}
+
+	private Node root = new Node('\0');
+
+	public boolean insert(String word) {
+	    return insert(word, root);
+	}
+
+	private boolean insert(String word, Node root) {
+    	root.prefixCount++;
+        if (word.length() >= 0 && root.wordCount > 0) {
+            return false;
+        }
+	    if (word.length() == 0) {
+	        if (root.prefixCount > 1) {
+	            return false;
+	        }
+	    	root.wordCount++;	    	
+	    	return true;
+	    }	    
+	    char ch = word.charAt(0);
+	    Node next = root.get(ch);	    
+	    if (next == null) {
+	        next = new Node(ch);	        
+	        root.put(ch, next);
+	    }	    
+	    return insert(word.substring(1), next);	    
+	}	
+
+	public static void main(String[] args) throws IOException {		
+
+		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
+		PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out));		
+
+		Trie trie = new Trie();        
+        int n = Integer.parseInt(in.readLine());
+
+        boolean bad = false;
+        while (n-- > 0) {
+            String word = in.readLine();  
+            bad = !trie.insert(word);            
+            if (bad) {
+                out.println("BAD SET\n"+word);    
+                break;
+            }
+        }
+
+
+        if (!bad) {
+            out.println("GOOD SET");
+        }        
+        out.close();
+
+	}	
+
+}