#0031

Valid Parentheses

EasyDSA15 min10 XP

Problem

Given a string containing only brackets, return True if every opening bracket is closed by the correct type in the correct order.

Why This Matters

This is the cleanest beginner example of why stacks exist: the last opened bracket must be the first one closed.

Function Signature

def is_valid(s):

Examples

Example 1

Inputs = "([]){}"

OutputTrue

Every closing bracket matches the most recent unmatched opening bracket.

Example 2

Inputs = "([)]"

OutputFalse

The ")" tries to close "(", but "[" is still open on top of the stack.

Constraints

String contains only bracket characters.
Empty string is valid.

CodePython

def is_valid(s):
    """
    Input example: s = "([]){}"
    Return: True
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    stack = []
    # write your code here
    return False

def is_valid(s):
    """
    Input example: s = "([]){}"
    Return: True
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    stack = []
    # write your code here
    return False

Visible browser tests run here when available.

Testcases2 visible / 4 hidden categories

Nested valid

Input"([]){}"

ExpectedTrue

Nested and adjacent groups are both handled.

Wrong order

Input"([)]"

ExpectedFalse

Correct counts are not enough; order matters.

Hidden Test Categories

Empty stringOnly opening bracketsOnly closing bracketsDeep nesting