Facebook Interview Question for SDE1s


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Wel... Actually you build a usual trie, but should take attention on next aspects:
1) Some words can be subwords of another, like: caw and cawboy, so you should have marker that will indicate complete words in a trie
2) '*' means that you should try to continue recursive backtracking search with any character on current level as well as with next character in pattern
3) Take into account that there can be '**' and more asterisk in line (I just replace such with single one)
4) Take into account that '*' could be last character in a pattern (and the only one character in a pattern).
Space complexity O(S*L), where S - number of words in trie, L - average length of word. Time complexity equals to number of nodes in a trie (in worst case of '*' pattern) should be O(S*L) (as we will visit each node one or two times in worst case).
It is tricky to take this all into account, but here is the code:

private static class Node {
    boolean isWord;
    Map<Byte,Node> children = new HashMap<Byte,Node>();    
  }
  
  private static class Trie {
    Node root=new Node();
    
    void add(String str) {
      Node node = root;
      for(int i=0;i<str.length();i++) {
        char ch=str.charAt(i);
        node=node.children.computeIfAbsent((byte)ch,s->new Node());
      }
      node.isWord=true;
    }
    
    static String preparePattern(String pattern) {
      return pattern.replaceAll("\\*+","*");
    }
    
    String stringFromPath(List<String> path) {
      return String.join("",path);
    }
    
    void searchRecursive(Node node, String pattern, int pos,
                         LinkedList<String> path, Set<String> found) {
      if(pos==pattern.length()) {
        if(node.isWord) 
          found.add(stringFromPath(path));
        return;
      }
      
      char ch = pattern.charAt(pos);
      if(ch=='*') {
        if(pos==pattern.length()-1 && node.isWord) {
          found.add(stringFromPath(path));
          if(node.children.size()==0)
            return;
        }
        
        for(Map.Entry<Byte,Node> entry : node.children.entrySet()) {
          Node nextNode = entry.getValue();
          path.addLast(String.valueOf((char)(entry.getKey().byteValue())));             
          searchRecursive(nextNode, pattern, pos, path, found);
          searchRecursive(nextNode, pattern, pos+1, path, found);
          path.removeLast();
        }
      } else {
        Node nextNode = node.children.get((byte)ch);
        if(nextNode!=null) {
          path.addLast(String.valueOf(ch));
          searchRecursive(nextNode, pattern, pos+1, path, found);
          path.removeLast();
        }
      }
    }
    
    Set<String> search(String pattern) {
      pattern = preparePattern(pattern);
      Set<String> found = new HashSet<String>();
      searchRecursive(root, pattern, 0, new LinkedList<String>(), found);
      return found;
    }
  }
  
  private static void doTest(Trie trie, String pattern) {
    System.out.println("Pattern: "+pattern+" : "+trie.search(pattern));
  }
  
  public static void main(String[] args) {
    Trie trie = new Trie();
    trie.add("car");
    trie.add("caw");
    trie.add("cauw");
    trie.add("caqweruw");
    trie.add("trie");
    trie.add("computer");
    trie.add("cawboy");
    doTest(trie,"c*w");
    doTest(trie,"ca*");
    doTest(trie,"c**w*");
    doTest(trie,"*r*");
    doTest(trie,"*");
  }

- Matviy Ilyashenko November 12, 2017 | Flag Reply
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public static void main(String args[]) {

            Trie root = new Trie();
            root.addWord("ca");
            root.addWord("cat");
            root.addWord("caw");
            root.addWord("cauw");
            root.addWord("cw");
            root.addWord("cramtowa");
            root.addWord("mccatorw");

            Set<String> result = new HashSet<>();
            FindWords(root, "c*a*", "", result);

            System.out.println(result);
    }

    private static void FindWords(Trie root, String word, String prefix, Set<String> result){

        if(word == null || word.length()==0 || root == null)
            return;

        StringBuilder sb = new StringBuilder();

        Trie current = root;
        for(int i=0;i<word.length(); i++){
            char c = word.charAt(i);
            if(c == '*'){
                String w = word.substring(i);
                char child = 'a';
                for(Trie t: current.childs()){
                    FindWords(t, w, prefix+sb.toString()+child, result);
                    child++;
                }
            }else{
                int index = c - 'a';
                if(current.childs()[index] != null){
                    current = current.childs()[index];
                    sb.append(c);
                }else{
                    return;
                }
            }
        }
        if(current.isKey()){
            System.out.println("Found String: "+prefix+sb);
            result.add(prefix+sb);
        }
    }

- incarose November 12, 2017 | Flag Reply
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of 0 vote

public static void main(String[] args) {

		Trie root = new Trie(false);
		add(root, "car".toCharArray());
		add(root, "caw".toCharArray());
		add(root, "cauw".toCharArray());

		match(root, "c*w".toCharArray(), 0, "", false);

	}

	// caw, c*w
	public static void match(Trie trie, char[] carr, int index, String str, boolean leaf) {

		if (index == carr.length) {
			if (leaf)
				System.out.println(str);
			return;
		}

		char c = carr[index];
		if (c == '*') {
			Trie[] next = trie.next;
			for (int i = 0; i < 26; i++) {
				if (next[i] != null) {
					match(next[i], carr, index + 1, str + (char)(i + 'a'), trie.leaf);
					match(next[i], carr, index, str + (char)(i + 'a'), trie.leaf);
				}
			}
		} else if (trie.next[c - 'a'] == null) {
			return;
		} else {
			match(trie.next[c - 'a'], carr, index + 1, str + carr[index], trie.leaf);
		}

	}

	// car
	public static void add(Trie trie, char[] carr) {
		int n = carr.length;
		for (int i = 0; i < n; i++) {
			if (trie.next[carr[i] - 'a'] == null) {
				Trie node = new Trie(false);
				trie.next[carr[i] - 'a'] = node;
				if (i == n - 2)
					node.leaf = true;
			}
			trie = trie.next[carr[i] - 'a'];
		}
	}

	static class Trie {

		Trie[] next = new Trie[26];
		boolean leaf;

		public Trie(boolean leaf) {
			this.leaf = leaf;
		}
	}

- sudip.innovates November 13, 2017 | Flag Reply


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