Uber QC Engineer Interview Questions and Answers

Regex for email validation

• Start with a string of characters followed by @ symbol

• Followed by a string of characters and a period

• End with a string of characters with a length of 2-6 characters

• Allow for optional subdomains separated by periods

• Disallow special characters except for . and _ in username

Print prime numbers in a given range and optimize the solution.

• Use Sieve of Eratosthenes algorithm to generate prime numbers efficiently

• Start with a boolean array of size n+1, mark all as true

• Loop through the array and mark all multiples of each prime as false

• Print all the indexes that are still marked as true

Find angle between hour and minute hand in a clock given the time.

• Calculate the angle made by the hour hand with respect to 12 o'clock position

• Calculate the angle made by the minute hand with respect to 12 o'clock position

• Find the difference between the two angles and take the absolute value

• If the angle is greater than 180 degrees, subtract it from 360 degrees to get the smaller angle

To un-hash a string, use a reverse algorithm to convert the hash back to the original string.

• Create a reverse algorithm that takes the hash as input and outputs the original string

• Use the same logic as the hash function but in reverse order

• If the hash function used a specific algorithm, use the inverse of that algorithm to un-hash the string

Print the level order traversal of binary tree in spiral form

• Perform level order traversal of the binary tree

• Alternate the direction of traversal for each level

• Use a stack to reverse the order of nodes in each level

• Print the nodes in the order of traversal

Find the maximum element in each subarray of size k in a given array.

• Iterate through the array from index 0 to n-k.

• For each subarray of size k, find the maximum element.

• Store the maximum elements in a separate array.

• Return the array of maximum elements.

To find the Kth largest element in two sorted arrays, we can use the merge step of merge sort algorithm.

• Merge the two arrays into a single sorted array using a modified merge sort algorithm.

• Return the Kth element from the merged array.

Merge two sorted arrays into one sorted array with expected time complexity of (m+n).

• Use a two-pointer approach to compare elements from both arrays and merge them into the first array.

• Start comparing elements from the end of both arrays and place the larger element at the end of the first array.

• Continue this process until all elements from the second array are merged into the first array.

The algorithm finds the position of the 3rd occurrence of 'B' in an n-ary tree from a given index in constant time complexity.

• Traverse the n-ary tree using a depth-first search (DFS) algorithm

• Keep track of the count of 'B' occurrences

• When the count reaches 3, return the current position

• If the end of the tree is reached before the 3rd 'B', return -1

Check if a given string is a composite of two words from a limited dictionary.

• Create a hash set of all the words in the dictionary.

• Iterate through all possible pairs of substrings in the given string.

• Check if both substrings are present in the hash set.

• If yes, return true. Else, return false.

Switch adjacent nodes in a single linked list.

• Traverse the linked list and swap adjacent nodes.

• Keep track of previous node to update its next pointer.

• Handle edge cases for first two nodes and last node.

• Example: 1->2->3->4 becomes 2->1->4->3.

Traverse only the left sub-tree of a binary search tree.

• Start at the root node

• If the left child exists, visit it and repeat the process

• If the left child does not exist, return to the parent node

• Continue until all nodes in the left sub-tree have been visited

Design an efficient data structure for two lifts in a building of n floors.

• Use a priority queue to keep track of the floors each lift is heading to

• Implement a scheduling algorithm to determine which lift to assign to a new request

• Consider adding a weight limit to each lift to prevent overloading

• Use a hash table to keep track of the current location of each lift

To find the maximum number that can be formed from the digits of an integer.

• Convert the integer to a string

• Sort the characters in descending order

• Join the sorted characters to form the maximum number