检查Python中的平衡括号

给定一个表达式字符串，编写一个Python程序来查找给定的字符串是否具有平衡括号。

例子：

Input : {[]{()}}
Output : Balanced

Input : [{}{}(]
Output : Unbalanced

方法#1：使用堆栈

检查平衡括号的一种方法是使用堆栈。每次遇到开括号时，将其压入堆栈，遇到闭括号时，将其与堆栈顶部匹配并弹出。如果栈最后是空的，则返回Balanced，否则返回Unbalanced。

# Python3 code to Check for 
# balanced parentheses in an expression
open_list = ["[","{","("]
close_list = ["]","}",")"]
  
# Function to check parentheses
def check(myStr):
    stack = []
    for i in myStr:
        if i in open_list:
            stack.append(i)
        elif i in close_list:
            pos = close_list.index(i)
            if ((len(stack) > 0) and
                (open_list[pos] == stack[len(stack)-1])):
                stack.pop()
            else:
                return "Unbalanced"
    if len(stack) == 0:
        return "Balanced"
    else:
        return "Unbalanced"
  
  
# Driver code
string = "{[]{()}}"
print(string,"-", check(string))
  
string = "[{}{})(]"
print(string,"-", check(string))
  
string = "((()"
print(string,"-",check(string))

输出：

{[]{()}} - Balanced
[{}{})(] - Unbalanced
((() - Unbalanced

方法#2：使用队列

首先将左括号映射到相应的右括号。使用 'i' 遍历给定的表达式，如果 'i' 是左括号，则追加到队列中，如果 'i' 是右括号，检查队列是否为空或 'i' 是队列的顶部元素，如果是，返回“不平衡”，否则“平衡”。

# Python3 code to Check for 
# balanced parentheses in an expression
def check(expression):
      
    open_tup = tuple('({[')
    close_tup = tuple(')}]')
    map = dict(zip(open_tup, close_tup))
    queue = []
  
    for i in expression:
        if i in open_tup:
            queue.append(map[i])
        elif i in close_tup:
            if not queue or i != queue.pop():
                return "Unbalanced"
    if not queue:
        return "Balanced"
    else:
        return "Unbalanced"
  
# Driver code
string = "{[]{()}}"
print(string, "-", check(string))
  
string = "((()"
print(string,"-",check(string))

输出：

{[]{()}} - Balanced
((() - Unbalanced

方法#3：基于消除
在每次迭代中，最里面的括号都会被消除（替换为空字符串）。如果我们最终得到一个空字符串，那么我们最初的字符串是平衡的；否则，不是。

# Python3 code to Check for 
# balanced parentheses in an expression
def check(my_string):
    brackets = ['()', '{}', '[]']
    while any(x in my_string for x in brackets):
        for br in brackets:
            my_string = my_string.replace(br, '')
    return not my_string
   
# Driver code
string = "{[]{()}}"
print(string, "-", "Balanced" 
      if check(string) else "Unbalanced")

输出：

{[]{()}} - Balanced