easyDSA

How do you check for valid/balanced parentheses?

Q: How do you check for valid/balanced parentheses?

**Intuition.** Brackets must close in the reverse order they opened — that's exactly what a **stack** models. Push every opening bracket; on a closing bracket, the top of the stack must be its matching opener. Valid means every close matched and the stack ends empty. scan "( [ ] )": push openers, match on closers ( [ ] ) <text x="300" y="40" fill="currentColor" font-s

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stackparentheses

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Stack-based validator

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def is_valid(s):
    pairs = {')': '(', ']': '[', '}': '{'}
    stack = []
    for c in s:
        if c in '([{':
            stack.append(c)
        elif not stack or stack.pop() != pairs[c]:
            return False
    return not stack


# --- demo ---
print(is_valid("()[]{}"))   # True
print(is_valid("(]"))       # False

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