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2. Valid Parentheses

easyAsked at Zoom

Determine if a string of brackets is properly nested and closed.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given a string containing only '()[]{}', determine if the input is valid. Brackets must be closed in the correct order and each open bracket has a matching close.

Constraints

  • 1 <= s.length <= 10^4
  • s consists only of bracket characters

Examples

Example 1

Input
s="()[]{}"
Output
true

Example 2

Input
s="(]"
Output
false

Approaches

1. Repeated replace

Repeatedly remove '()', '[]', '{}'.

Time
O(n^2)
Space
O(n)
while (s.includes('()')||s.includes('[]')||s.includes('{}'))
  s = s.replace('()','').replace('[]','').replace('{}','');
return s==='';

Tradeoff:

2. Stack

Push opens, pop on close and check match. Empty stack at the end means valid.

Time
O(n)
Space
O(n)
function isValid(s) {
  const map = { ')': '(', ']': '[', '}': '{' };
  const stack = [];
  for (const ch of s) {
    if (!(ch in map)) stack.push(ch);
    else if (stack.pop() !== map[ch]) return false;
  }
  return stack.length === 0;
}

Tradeoff:

Zoom-specific tips

Zoom interviewers often ask candidates to extend this into protocol-frame validation (RTP/SIP packet bracket-like delimiters), so anchor your stack analogy to streaming-protocol parsing.

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Output

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