Skip to main content

2. Valid Parentheses

easyAsked at Swiggy

Check whether a string of brackets is well-formed.

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

Problem

Given a string containing only '()[]{}', determine whether the input string is valid. Brackets must close in correct order and types must match.

Constraints

  • 1 <= s.length <= 10^4
  • s contains only bracket characters

Examples

Example 1

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

Example 2

Input
s="(]"
Output
false

Approaches

1. Brute force replace

Repeatedly remove '()','[]','{}' until stable; check empty.

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 on closers and verify match.

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

Tradeoff:

Swiggy-specific tips

Swiggy uses this as a fluency check; mention validating order-modifier nesting (combos, add-ons) as a real production analogue.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Valid Parentheses and other Swiggy interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →