2. Valid Parentheses

easyAsked at Ramp

Determine if a string of brackets is valid (every open has a matching close in the right order).

By Alex Chen, Founder, InterviewChamp.AI · Last verified 2026-05-20

Problem

Given a string of characters '()[]{}', return true if every opening bracket has a corresponding closing bracket in the correct order and nesting.

Constraints

1 <= s.length <= 10^4
s consists only of '()[]{}'

Examples

Example 1

Input

s = "()[]{}"

Output

true

Example 2

Input

s = "(]"

Output

false

Approaches

1. Replace pairs (brute)

Repeatedly remove matching empty pairs until stable, then check empty.

Time: O(n^2)
Space: O(n)

while (s.includes('()')||s.includes('[]')||s.includes('{}')) s = s.replace(/\(\)|\[\]|\{\}/g,'');
return s.length===0;

Tradeoff:

2. Stack

Push opens, pop and verify on closes; valid iff stack empty at end. Linear time, single pass.

Time: O(n)
Space: O(n)

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

Tradeoff:

Ramp-specific tips

Ramp uses bracket-matching as a warmup before pivoting into validating nested approval-policy DSL expressions, so structure your stack solution to be easily extended to typed tokens.

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 Ramp interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →