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2. Valid Parentheses

easyAsked at Wix

Validate balanced brackets using a stack; Wix uses this for template-tag matching in their HTML editor.

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

Problem

Given a string s containing the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. Brackets must close in 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

Repeatedly remove matching pairs until none left.

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 openers, pop and match on closers.

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

Tradeoff:

Wix-specific tips

Wix asks this with a twist about validating their Velo template syntax — mention how the same stack pattern detects malformed component nesting in user-built sites.

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Output

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