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Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

What difficulty level is this interview question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Grammarly.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Grammarly during technical interviews.

Remove adjacent duplicates and handle tree input

Quick Overview

This question evaluates string-processing and tree-construction skills, including efficient removal of adjacent or k-sized duplicate groups in strings and building a binary tree from a level-order array to compute properties such as the sum of left leaves.

You are asked three related coding questions.

1) Remove adjacent duplicates (repeatedly)

Given a string s (lowercase English letters), repeatedly remove any pair of adjacent equal characters until no such pair exists.

Input: s
Output: the final string after all removals

Example:

s = "abbaca" → remove bb → aaca → remove aa → ca

Constraints (typical): 1 <= |s| <= 1e5.

2) Follow-up: remove groups of size k

Given a string s and an integer k, repeatedly remove any group of exactly k adjacent equal characters until no more removals are possible.

Input: s , k
Output: final string

Example:

s = "deeedbbcccbdaa", k = 3 → output "aa"

Constraints (typical): 1 <= |s| <= 1e5, 2 <= k <= 1e4.

3) Tree problem, but input is an array (must build the tree)

You are given a binary tree in level-order array form (not TreeNode objects). null indicates a missing child. Build the binary tree and compute:

The sum of all left leaf nodes (a left leaf is a leaf node that is the left child of its parent).

Input: array arr of integers and null s, in level-order
Output: integer sum

Example:

arr = [3,9,20,null,null,15,7] → left leaves are 9 and 15 → output 24

Notes: You must construct the tree from the array representation before computing the answer.

Quick Overview

1) Remove adjacent duplicates (repeatedly)

Given a string s (lowercase English letters), repeatedly remove any pair of adjacent equal characters until no such pair exists.

Input: s

Output: the final string after all removals

Example:

s = "abbaca" → remove bb → aaca → remove aa → ca

Constraints (typical): 1 <= |s| <= 1e5.

3) Tree problem, but input is an array (must build the tree)

You are given a binary tree in level-order array form (not TreeNode objects). null indicates a missing child. Build the binary tree and compute:

The sum of all left leaf nodes (a left leaf is a leaf node that is the left child of its parent).

Input: array arr of integers and null s, in level-order

Output: integer sum

Example:

arr = [3,9,20,null,null,15,7] → left leaves are 9 and 15 → output 24

Notes: You must construct the tree from the array representation before computing the answer.

Remove adjacent duplicates and handle tree input

Quick Overview

1) Remove adjacent duplicates (repeatedly)

2) Follow-up: remove groups of size k

3) Tree problem, but input is an array (must build the tree)

Submit Your Answer to Earn 20XP

Remove adjacent duplicates and handle tree input

Quick Overview

1) Remove adjacent duplicates (repeatedly)

2) Follow-up: remove groups of size k

3) Tree problem, but input is an array (must build the tree)

Submit Your Answer to Earn 20XP