Balanced Smileys

Programming challenge description:

Credits: This problem appeared in the Facebook Hacker Cup 2013 Hackathon. Your friend John uses a lot of emoticons when you talk to him on Messenger. In addition to being a person who likes to express himself through emoticons, he hates unbalanced parenthesis so much that it makes him go :(. Sometimes he puts emoticons within parentheses, and you find it hard to tell if a parenthesis really is a parenthesis or part of an emoticon. A message has balanced parentheses if it consists of one of the following: - An empty string "" - One or more of the following characters: 'a' to 'z', ' ' (a space) or ':' (a colon) - An open parenthesis '(', followed by a message with balanced parentheses, followed by a close parenthesis ')'. - A message with balanced parentheses followed by another message with balanced parentheses. - A smiley face ":)" or a frowny face ":(" Write a program that determines if there is a way to interpret his message while leaving the parentheses balanced.

Input:

Your program should read lines from standard input. Each line contains a message that you got from John.

Output:

Print out the string "YES"/"NO" (all quotes for clarity only) stating whether or not it is possible that the message had balanced parentheses

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.nio.charset.StandardCharsets;

public class Main { /** * Iterate through each line of input. */ public static void main(String[] args) throws IOException { InputStreamReader reader = new InputStreamReader(System.in, StandardCharsets.UTF_8); BufferedReader in = new BufferedReader(reader); String line; while ((line = in.readLine()) != null) { System.out.println(line); } } }