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Solve tree view and parentheses cleanup

MetaSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenCoding & Algorithms

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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.

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]
  1. 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)