Python: Validity of a string of parentheses

Last update on April 21 2025 12:54:31 (UTC/GMT +8 hours)

3. Check Validity of a String of Parentheses

Write a Python class to check the validity of a string of parentheses, '(', ')', '{', '}', '[' and ']. These brackets must be closed in the correct order,
for example "()" and "()[]{}" are valid but "[)", "({[)]" and "{{{" are invalid.

Sample Solution:

Python Code:

class py_solution:
   def is_valid_parenthese(self, str1):
        stack, pchar = [], {"(": ")", "{": "}", "[": "]"}
        for parenthese in str1:
            if parenthese in pchar:
                stack.append(parenthese)
            elif len(stack) == 0 or pchar[stack.pop()] != parenthese:
                return False
        return len(stack) == 0

print(py_solution().is_valid_parenthese("(){}[]"))
print(py_solution().is_valid_parenthese("()[{)}"))
print(py_solution().is_valid_parenthese("()"))

Sample Output:

True                                                                                                          
False                                                                                                         
True

Pictorial Presentation:

Python: Validity of a string of parentheses.

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python class that uses a stack to verify if a string containing '()', '{}', and '[]' is balanced and valid.
Write a Python class that implements recursive descent parsing to check the validity of nested parentheses in a string.
Write a Python class that uses a dictionary to match opening and closing brackets and determines the string's validity.
Write a Python class that handles edge cases (empty string, single bracket) and returns a boolean indicating whether the parentheses are correctly balanced.

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