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2. Valid Parentheses

easyAsked at Gojek

Given a string containing brackets, determine if all brackets are properly closed in the correct order.

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

Problem

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

Repeatedly remove matched pairs until stable.

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, pop and compare on closers. Reject early on mismatch.

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

Tradeoff:

Gojek-specific tips

Gojek interviewers like stack-based reasoning since their order-state and payment-flow workflows nest deeply across ride, food, and wallet services.

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