How do I approach Coding & Algorithms interview questions?

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 Onsite rounds at Meta.

What role is this question designed for?

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

Solve three array/string/graph coding tasks

Q: Solve three array/string/graph coding tasks

This set of three coding tasks evaluates proficiency in fundamental data structures and algorithms, covering multi-way array merging, custom character ordering and grouping, and graph cloning with correct handling of cycles and references.

You are given three separate coding tasks. Implement each as a function.

1) Merge three sorted arrays

Input: Three integer arrays A, B, C, each sorted in non-decreasing order (may contain duplicates, may be empty).

Output: A single array containing all elements from A, B, and C in non-decreasing order.

Constraints (typical): Total length up to ~1e5.

Example:

A = [1, 4, 4] , B = [2, 6] , C = [0, 4, 10]
Output: [0, 1, 2, 4, 4, 4, 6, 10]

2) Sort characters by a given custom order

You are given a string order that defines a custom ordering of (some) characters, and a string s to sort.

Rules:

Characters that appear in order must appear in the output in the same relative order as in order .
If a character appears multiple times in s , all its occurrences should be grouped together.
Characters in s that do not appear in order should appear at the end (you may keep their relative order from s , or specify/implement a consistent rule).

Input: order (string), s (string)

Output: A reordered string.

Example:

order = "cba" , s = "abcdabc"
Output: "ccbb aa dd" without spaces → e.g. "ccbbaad" (all c first, then b , then a , then the remaining characters like d ).

3) Deep copy (clone) a graph

Given a reference to a node in a connected, undirected graph, return a deep copy (clone) of the entire graph.

Assume each node has:

an integer val
a list of neighbor node references neighbors

Requirements:

The cloned graph must contain entirely new nodes (no pointer/reference sharing with the original).
Adjacency (edges) must be preserved.
Handle cycles correctly.

Input: A node reference node (or null).

Output: A node reference to the cloned node corresponding to the input node (or null).

Edge cases to consider: null input, single-node graph, cycles, self-loops.

You are given three separate coding tasks. Implement each as a function.

1) Merge three sorted arrays

Input: Three integer arrays A, B, C, each sorted in non-decreasing order (may contain duplicates, may be empty).

Output: A single array containing all elements from A, B, and C in non-decreasing order.

Constraints (typical): Total length up to ~1e5.

Example:

A = [1, 4, 4] , B = [2, 6] , C = [0, 4, 10]
Output: [0, 1, 2, 4, 4, 4, 6, 10]

2) Sort characters by a given custom order

You are given a string order that defines a custom ordering of (some) characters, and a string s to sort.

Rules:

Characters that appear in order must appear in the output in the same relative order as in order .
If a character appears multiple times in s , all its occurrences should be grouped together.
Characters in s that do not appear in order should appear at the end (you may keep their relative order from s , or specify/implement a consistent rule).

Input: order (string), s (string)

Output: A reordered string.

Example:

order = "cba" , s = "abcdabc"
Output: "ccbb aa dd" without spaces → e.g. "ccbbaad" (all c first, then b , then a , then the remaining characters like d ).

3) Deep copy (clone) a graph

Given a reference to a node in a connected, undirected graph, return a deep copy (clone) of the entire graph.

Assume each node has:

an integer val
a list of neighbor node references neighbors

Requirements:

The cloned graph must contain entirely new nodes (no pointer/reference sharing with the original).
Adjacency (edges) must be preserved.
Handle cycles correctly.

Input: A node reference node (or null).

Output: A node reference to the cloned node corresponding to the input node (or null).

Edge cases to consider: null input, single-node graph, cycles, self-loops.

Solve three array/string/graph coding tasks

Quick Overview

1) Merge three sorted arrays

2) Sort characters by a given custom order

3) Deep copy (clone) a graph

Comments (0)

Solve three array/string/graph coding tasks

Quick Overview

1) Merge three sorted arrays

2) Sort characters by a given custom order

3) Deep copy (clone) a graph

Comments (0)