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2. Valid Parentheses

easyAsked at Indeed

Validate that bracket pairs are properly nested and closed — Indeed uses it to gauge stack fluency before resume-parser and search-query syntax problems.

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

Problem

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input is valid when brackets are closed by the same type and in the right order.

Constraints

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

Examples

Example 1

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

Example 2

Input
s = "(]"
Output
false

Approaches

1. Brute force replace

Repeatedly strip matching pairs until none remain.

Time
O(n^2)
Space
O(n)
while (s.includes('()') || s.includes('[]') || s.includes('{}')) {
  s = s.replace('()','').replace('[]','').replace('{}','');
}
return s.length === 0;

Tradeoff:

2. Stack

Push openers and pop on closers, checking the top matches the expected pair.

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

Tradeoff:

Indeed-specific tips

Indeed wants the stack-popping logic mapped to validating search-query operators (parens around AND/OR clauses) — mention that connection during your walkthrough.

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Output

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