Validate whether brackets are properly nested

## Problem: Validate a bracket sequence Given a string `s` consisting only of the characters `'('`, `')'`, `'{'`, `'}'`, `'['`, `']'`, determine whether the string is **valid**. A string is valid if: - Every opening bracket has a corresponding closing bracket of the **same type**. - Brackets are closed in the **correct order** (properly nested). - An empty string is considered valid. ### Input - A string `s` (length `0..10^5`) containing only the six bracket characters. ### Output - Return `true` if `s` is valid, otherwise return `false`. ### Examples - `s = "()"` → `true` - `s = "()[]{}"` → `true` - `s = "(]"` → `false` - `s = "([)]"` → `false` - `s = "{[]}"` → `true` ### Follow-up discussion prompts (as in interview) - What is the time and space complexity? - Can you optimize for space or early termination? - What edge cases would you test?