CodeSignal Technical Assessment Array and String Manipulation Questions and Answers

Question 1

A programmer needs to reverse the order of words in a given string, where words are separated by single spaces.
For example, 'codesignal is awesome' should become 'awesome is codesignal'.
Which of the following approaches is the MOST efficient in terms of time complexity for a typical programming language?

Accepted Answer

Split the string by spaces into an array of words, reverse the array, and then join the words back together with spaces.

Answer

Iterate through the string from end to start, building each word character by character, and append them to a new string.

Answer

Use a stack data structure. Push each word onto the stack, and then pop them off one by one to form the new string.

Answer

Reverse the entire string, and then iterate through the reversed string to reverse each individual word in place.

Question 2

You are given a task to find the first non-repeating character in a string. For the string 'aabbcdeff', the correct output is 'c'. Which data structure is most suitable for solving this problem efficiently by tracking character counts?

Accepted Answer

A hash map (or dictionary)

Answer

A queue

Answer

A stack

Answer

A 2D array

Question 3

A developer is implementing a function `rotateArray(nums, k)` that rotates an array `nums` to the right by `k` steps, where `k` is non-negative. If `nums = [1, 2, 3, 4, 5, 6, 7]` and `k = 3`, the result should be `[5, 6, 7, 1, 2, 3, 4]`. What is a potential issue with the expression `k = k % nums.length;` if it's used at the beginning of the function?

Accepted Answer

There is no issue; this is a standard and necessary optimization.

Answer

It will cause an error if k is larger than the array length.

Answer

It doesn't correctly handle the case where k is 0.

Answer

It fails to account for negative values of k.

Question 4

Which of the following statements about string and array manipulation is generally TRUE across most programming languages like Python, Java, and JavaScript?

Accepted Answer

Strings can often be treated as arrays of characters, allowing for indexed access to individual characters.

Answer

Arrays have a fixed size after creation and cannot be expanded.

Answer

Strings are mutable, meaning their characters can be changed in place after creation.

Answer

Accessing an element in an array by its index is typically an O(n) operation.

Question 5

In a scenario where you need to check if a string is a palindrome (reads the same forwards and backwards), which algorithm offers the best time complexity?

Accepted Answer

Use two pointers, one at the beginning and one at the end, moving towards the center and comparing characters.

Answer

Create a reversed copy of the string and compare it to the original.

Answer

Use a stack: push the first half of the string onto the stack, then pop and compare with the second half.

Answer

Sort the characters of the string and compare it with the original sorted string.

Question 6

You are given two sorted arrays, `arr1` and `arr2`, and you need to merge them into a single sorted array. This is a common operation in algorithms. What is the time complexity of the most efficient approach to solve this problem?

Accepted Answer

O(n + m)

Answer

O(n*m)

Answer

O(n log n)

Answer

O(n^2)