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2. Valid Parentheses

easyAsked at Freshworks

Determine if a string of brackets is correctly opened and closed.

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

Problem

Given a string containing only the characters '()[]{}', determine if it is valid. Open brackets must close in the correct order.

Constraints

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

Examples

Example 1

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

Example 2

Input
s="(]"
Output
false

Approaches

1. Naive 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 and match on closes. Stack must be empty at end.

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

Tradeoff:

Freshworks-specific tips

Freshworks interviewers care about edge cases like empty strings and unmatched closers — name them aloud.

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Output

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