Parentheses pairing ({}[]()<>) issue

Question

I want to be able to pair up all parentheses in a string, if they aren\'t paired then then they get their index number and False. It seems like it is repeating some values over

Answer 1

Try this:

def matched(s):
stack=[]
open,close="(",")" 
for i in s:
    if i in open:
        stack.append(i)
    if i in close:
        if len(stack)==0:
            return(False)
        else:   
            stack.pop()
if len(stack):
    return(False)
else:
    return(True)

Answer 2

You can adapt my code to a similar question:

def Evaluate(str):
  stack = []
  pushChars, popChars = "<({[", ">)}]"
  for c in str :
    if c in pushChars :
      stack.append(c)
    elif c in popChars :
      if not len(stack) :
        return False
      else :
        stackTop = stack.pop()
        balancingBracket = pushChars[popChars.index(c)]
        if stackTop != balancingBracket :
          return False
    else :
      return False
  return not len(stack)

Answer 3

First we will scan the string from left to right, and every time we see an opening parenthesis we push it to a stack, because we want the last opening parenthesis to be closed first. (Remember the FILO structure of a stack!) Then, when we see a closing parenthesis we check whether the last opened one is the corresponding closing match, by popping an element from the stack. If it’s a valid match, then we proceed forward, if not return false. Code: https://gist.github.com/i143code/51962bfb1bd5925f75007d4dcbcf7f55