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2. Valid Parentheses

easyAsked at GoDaddy

Determine whether a string of brackets is properly nested and balanced.

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 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 parentheses only '()[]{}'

Examples

Example 1

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

Example 2

Input
s = "(]"
Output
false

Approaches

1. Brute force replace

Repeatedly remove '()', '[]', '{}' substrings 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; on a closer, pop and compare. End must leave the stack empty.

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

Tradeoff:

GoDaddy-specific tips

GoDaddy uses parentheses validation as a stand-in for parsing DNS zone files where unbalanced quote/brace pairs make a record un-publishable.

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Output

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