Solve tree view and parentheses cleanup
Company: Meta
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
Solve the following two algorithm problems.
1. Right-side view of a binary tree
Given the root of a binary tree, return the values of the nodes that would be visible if you looked at the tree from its right side, listed from top to bottom.
Example:
- Input: root = [1,2,3,null,5,null,4]
- Output: [1,3,4]
2. Remove the minimum invalid parentheses
Given a string `s` containing lowercase English letters and the characters `(` and `)`, remove the minimum number of parentheses so that the resulting string is valid.
A string is valid if:
- every opening parenthesis has a matching closing parenthesis,
- parentheses are properly ordered,
- letters may appear anywhere and do not affect validity.
Return any valid string after the minimum removals.
Examples:
- Input: `a)b(c)d`
Output: `ab(c)d`
- Input: `))( (`
Output: ``
- Input: `(a(b(c)d)`
Output: `a(b(c)d)`
Quick Answer: This question evaluates binary tree traversal and view-extraction skills for the right-side view problem and string-processing and minimal-edit balancing for the parentheses cleanup, probing competency in data-structure traversal, state tracking, and correctness under edge cases.