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2. Valid Parentheses

easyAsked at Booking

Use a stack to validate matching brackets — Booking screens this to confirm you can model nested filter expressions in search.

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

Problem

Given a string containing the characters '(', ')', '{', '}', '[', ']', determine if the input string is valid: open brackets are closed by the same type in the correct order.

Constraints

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

Examples

Example 1

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

Example 2

Input
s = "(]"
Output
false

Approaches

1. Brute force replace

Repeatedly remove '()', '[]', '{}' until none left.

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 opens, pop on close and verify it matches the expected type.

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

Tradeoff:

Booking-specific tips

Booking values clean handling of nested availability calendar expressions — connect the stack to validating nested search-filter trees.

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Output

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