CheckIO - Electronic Station Challenge 1 : Brackets

checkio.3.01.brackets.py

# CheckIO - Electronic Station Challenge 1 : Brackets
# http://checkio.org

# You are given an expression with numbers, brackets and operators. 
# For this task only the brackets matter. Brackets come in three flavors: "{}" "()" or "[]". 
# Brackets are used to determine scope or to restrict some expression. 
# If a bracket is open, then it must be closed with a closing bracket of the same type. 
# The scope of a bracket must not intersected by another bracket. 
# For this task, you should to make a decision to correct an expression or not based on the brackets. 
# Do not worry about operators and operands.
# Input: An expression with different of types brackets. A string (unicode).
# Output: The correctness the expression or don’t. A boolean.
# Precondition: There are only brackets ("{}" "()" or "[]"), digits or operators ("+" "-" "*" "/").

def checkio(expression):
    BRACKETS="()[]{}"
    openBrackets=[]
    for b in expression:
        if BRACKETS.count(b)==0: continue   # No bracket character
        if "([{".count(b): openBrackets+=b  # Adding open bracket
        else:   # if char is a close bracket...
            if not openBrackets: return False                   # Empty open brackets array case
            lastBracketIndex=BRACKETS.index(openBrackets[-1])   
            if b!=BRACKETS[lastBracketIndex+1]: return False    # Different type of bracket case
            else: openBrackets=openBrackets[:-1]                # Removing bracket from array...
    if openBrackets: return False                               # Some open bracket remaining case
    return True

#These "asserts" using only for self-checking and not necessary for auto-testing
if __name__ == '__main__':
    assert checkio("((5+3)*2+1)") == True, "Simple"
    assert checkio("{[(3+1)+2]+}") == True, "Different types"
    assert checkio("(3+{1-1)}") == False, ") is alone inside {}"
    assert checkio("[1+1]+(2*2)-{3/3}") == True, "Different operators"
    assert checkio("(({[(((1)-2)+3)-3]/3}-3)") == False, "One is redundant"
    assert checkio("2+3") == True, "No brackets, no problem"