## Problem A — Validate parentheses Given a string `s` containing only the characters `'('`, `')'`, `'['`, `']'`, `'{'`, `'}'`, determine whether 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 closing bracket has a corresponding previously-opened bracket. **Input:** `s` (string) **Output:** `true` if `s` is valid, otherwise `false`. **Example** - `s = "()[]{}"` → `true` - `s = "([)]"` → `false` **Constraints (typical):** `1 <= |s| <= 10^4` --- ## Problem B — k-th largest element using a heap Given an integer array `nums` and an integer `k`, return the **k-th largest** element in the array. Notes: - “k-th largest” refers to the element that would appear at index `k-1` if the array were sorted in descending order. - Duplicates count as separate elements. **Input:** `nums` (array of integers), `k` (integer) **Output:** an integer, the k-th largest element. **Example** - `nums = [3,2,1,5,6,4], k = 2` → `5` **Constraints (typical):** - `1 <= n <= 10^5` - `1 <= k <= n` - `nums[i]` fits in 32-bit signed int