ProblemYour 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.I'm working on this balanced smileys checking algorithm, and my current solution is very naive, just enumerate all possible ways to interpret :) and :(. I'm wondering if any smarter ideas in terms of algorithm time complexity perspective.def procee_raw_string(source):    result = []    for i,v in enumerate(source):        if v == '(':            if i > 0 and source[i-1] == ':':                result.append(source[i-1:i+1])            else:                result.append(v)        elif v == ')':            if i>0 and source[i-1] == ':':                result.append(source[i-1:i+1])            result.append(')')    return ''.join(result)def check_balance(source):    stack = []    for s in source:        if s == '(':            stack.append(s)        else: # s is ')'            if len(stack) == 0 or stack[-1] != '(':                return False            else:                stack.pop(-1)    if len(stack) > 0:        return False    return Truedef generate_balance_string(source, index, prefix, result):    if index >= len(source):        result.append(prefix[:])        return    if source[index] == ':' and source[index+1] == '(':        prefix.append('(')        generate_balance_string(source, index+2, prefix, result)        prefix.pop(-1)        generate_balance_string(source, index+2, prefix, result)    elif source[index] == ':' and source[index+1] == ')':        prefix.append(')')        generate_balance_string(source, index+2, prefix, result)        prefix.pop(-1)        generate_balance_string(source, index+2, prefix, result)    elif source[index] == '(':        prefix.append('(')        generate_balance_string(source, index+1, prefix, result)        prefix.pop(-1)    elif source[index] == ')':        prefix.append(')')        generate_balance_string(source, index+1, prefix, result)        prefix.pop(-1)if __name__ == __main__:    raw_smile_string = 'abc(b:)cdef(:()'    process_string = procee_raw_string(raw_smile_string)    result = []    generate_balance_string(process_string, 0, [], result)    for r in result:        print check_balance(r)Additional thoughts,I am not sure if we could do such simple check for balance?If number of close parenthesis (excluding the smileys) are ever more than the number of open parenthesis, then parentheses are not balanced.If number of open parenthesis at the end (excluding the frowns) are more than the close ones, then also the parentheses are not balanced.
Balanced smileys check algorithm
python;python 2.7;balanced delimiters