DSA · Stack · #02

Valid Parentheses

Module 4 · difficulty 2/5·⏱ 30:00starts on first keystroke

Given a string `s` containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid. A string is valid if: - Open brackets are closed by the same type of brackets. - Open brackets are closed in the correct order. - Every close bracket has a corresponding open bracket of the same type.

Examples

s = "()" → true
s = "()[]{}" → true
s = "(]" → false
s = "([)]" → false — order matters — close must match the most recent open
s = "]" → false — close before any open

Constraints

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

Session phases

A · Clarify

B · Approach

C · Complexity

D · Edges

E · Code

F · Tradeoff

G · Score

Phase A — Clarify

Ask questions about input bounds, types, and edge constraints.

Ask the coach clarifying questions about the problem.

When you've covered this phase, advance to the next.