Top 30 Most Common Machine Coding Round Questions You Should Prepare For
Written by
James Miller, Career Coach
Navigating the technical interview landscape can be challenging, especially when you encounter the dreaded machine coding round questions. These aren't just theoretical puzzles; they test your ability to translate problem descriptions into working, efficient code within a limited timeframe. Mastering machine coding round questions is crucial for success in interviews at top tech companies. This article delves into the most frequently encountered problems in machine coding rounds, offering insights into why they are asked, how to approach them, and what a successful answer looks like. Preparing thoroughly for these types of machine coding round questions will significantly boost your confidence and performance. We'll cover a diverse range of topics, from fundamental data structures like arrays and linked lists to essential algorithms like sorting, searching, and dynamic programming. Understanding the underlying principles and common patterns behind these machine coding round questions is key to solving variations on the spot. Get ready to sharpen your coding skills and tackle those challenging machine coding round questions head-on.
What Are machine coding round questions?
Machine coding round questions are a type of technical interview problem that requires candidates to write functional code to solve a specific problem within a given time frame, typically 60-90 minutes. Unlike pure data structure and algorithm rounds that might focus on theory or pseudocode, machine coding round questions demand a complete, runnable solution, often with test cases. These problems usually involve integrating multiple concepts, such as data structures, algorithms, and object-oriented design principles. They are designed to simulate real-world coding tasks, assessing not just your algorithmic knowledge but also your coding style, error handling, and ability to produce clean, maintainable code under pressure. Successfully tackling machine coding round questions demonstrates practical programming proficiency essential for software development roles. The complexity of these machine coding round questions can vary, but they generally require more than a trivial solution.
Why Do Interviewers Ask machine coding round questions?
Interviewers use machine coding round questions to evaluate a candidate's practical coding skills, not just theoretical knowledge. They want to see if you can translate an idea into working code, handle edge cases, and write code that is readable and maintainable. Machine coding round questions reveal your approach to problem-solving, how you structure your code, your debugging process, and your ability to work efficiently under time constraints. It assesses your command over data structures and algorithms in a practical setting. Companies understand that being able to solve theoretical problems is different from building functional software, and machine coding round questions bridge this gap. They provide a realistic glimpse into your daily work habits as a software engineer. Strong performance on machine coding round questions signals that you can be productive from day one.
Reverse an Array In-Place
Find K-th Largest Element in an Array
Reverse a Linked List
Detect Loop in a Linked List
Merge Two Sorted Arrays
Kadane’s Algorithm (Maximum Subarray Sum)
Find Missing Number in Array
Count Triplets with Given Sum
Check if String is Rotated by Two Places
Remove Duplicates from a String
Implement atoi (String to Integer Conversion)
Spiral Matrix Traversal
Longest Palindromic Substring
Implement strstr (Substring Search)
Stock Buy and Sell for Maximum Profit
Intersection Point in Y Shaped Linked Lists
Detect and Remove Loop in Linked List
Trapping Rain Water
Count Inversions in Array
Chocolate Distribution Problem
Check if Palindrome
Permutations of a String
Reverse Words in a String
Find Middle Element of Linked List
Merge Intervals
Balanced Parentheses
Convert Roman Number to Integer
Implement Queue using Stacks
Find All Anagrams in a String
Kth Smallest Element in an Array
Preview List
1. Reverse an Array In-Place
Why you might get asked this:
Tests understanding of in-place algorithms and basic array manipulation without using extra space.
How to answer:
Use two pointers, one starting from the beginning and the other from the end, swapping elements until they meet in the middle.
Example answer:
Initialize left=0, right=arr.length-1. While left < right, swap arr[left] and arr[right], increment left, decrement right.
2. Find K-th Largest Element in an Array
Why you might get asked this:
Evaluates knowledge of sorting algorithms, heap data structure, or selection algorithms like Quickselect.
How to answer:
A simple approach is to sort and pick the element at index k-1. More efficient is using a min-heap or Quickselect partition logic.
Example answer:
Sort the array in descending order. The element at index k-1 is the K-th largest. For {3,2,1,5,6,4}, k=2, sorted {6,5,4,3,2,1}, result is 5.
3. Reverse a Linked List
Why you might get asked this:
A fundamental test of linked list manipulation, pointer handling, and iterative/recursive approaches.
How to answer:
Iterate through the list, maintaining pointers to the previous, current, and next nodes, reversing the 'next' pointer at each step.
Example answer:
Iterate: prev = null, current = head. In loop: nextnode = current.next, current.next = prev, prev = current, current = nextnode. prev becomes new head.
4. Detect Loop in a Linked List
Why you might get asked this:
Tests linked list traversal and the ability to detect cycles, often using Floyd's Cycle Detection algorithm.
How to answer:
Use two pointers, one slow (moves 1 step) and one fast (moves 2 steps). If they meet, a loop exists.
Example answer:
Initialize slow=head, fast=head. While fast and fast.next exist, move slow one step and fast two steps. If slow === fast, return true.
5. Merge Two Sorted Arrays
Why you might get asked this:
Checks ability to handle multiple data streams and merge them efficiently while maintaining sorted order.
How to answer:
Use two pointers, one for each array, comparing elements and adding the smaller one to a new result array until both are exhausted.
Example answer:
Pointers i=0, j=0 for arr1, arr2. While i < m or j < n, compare arr1[i] and arr2[j], add smaller to result, increment respective pointer.
6. Kadane’s Algorithm (Maximum Subarray Sum)
Why you might get asked this:
A classic dynamic programming problem testing optimization and tracking current vs. global maximums.
How to answer:
Iterate through the array, keeping track of the maximum sum ending at the current position and the overall maximum sum found so far.
Example answer:
Initialize maxsofar = maxendinghere = 0. Loop through array: maxendinghere = max(arr[i], maxendinghere + arr[i]), maxsofar = max(maxsofar, maxendinghere).
7. Find Missing Number in Array
Why you might get asked this:
Tests basic array properties and mathematical or bitwise approaches for finding anomalies.
How to answer:
Sum all numbers from 1 to N, then sum numbers in the array. The difference is the missing number. Alternatively, XOR all numbers 1-N with array elements.
Example answer:
Calculate expected sum: N*(N+1)/2. Calculate actual sum of array elements. Return expected sum - actual sum.
8. Count Triplets with Given Sum
Why you might get asked this:
Evaluates ability to combine sorting or hashing with two-pointer or brute-force techniques to find combinations.
How to answer:
Sort the array. Iterate through each element, then use a two-pointer approach on the remaining elements to find pairs that sum to target - current_element.
Example answer:
Sort the array. For each element a[i], use pointers left=i+1, right=n-1. If a[i] + a[left] + a[right] == sum, count and adjust pointers. If sum too low/high, adjust accordingly.
9. Check if String is Rotated by Two Places
Why you might get asked this:
Tests string manipulation, shifting, and comparison logic.
How to answer:
Create two potential rotations of the first string: one shifted left by two and one shifted right by two. Compare these with the second string.
Example answer:
For string "abcde", left shift 2 is "cdeab", right shift 2 is "deabc". Compare these with the target string.
10. Remove Duplicates from a String
Why you might get asked this:
Tests string processing and using auxiliary data structures (like hash sets) for tracking seen elements.
How to answer:
Iterate through the string. Use a hash set (or boolean array) to keep track of characters already encountered. Append characters not yet seen to a result string.
Example answer:
Initialize empty result string and empty hash set. Iterate through input string characters. If char not in hash set, add to set and result string.
11. Implement atoi (String to Integer Conversion)
Why you might get asked this:
Assesses ability to parse strings, handle edge cases (leading/trailing spaces, signs, overflow, invalid characters), and implement numerical conversion.
How to answer:
Trim whitespace, handle optional sign, iterate through digits, convert characters to numerical values, accumulate result, and check for overflow.
Example answer:
Skip leading spaces. Check for '+' or '-'. Iterate through digits, converting char - '0' and adding to result res = res * 10 + digit. Check against max/min integer values.
12. Spiral Matrix Traversal
Why you might get asked this:
Tests matrix traversal logic and managing boundary conditions for multiple directions.
How to answer:
Maintain four boundary pointers (top, bottom, left, right). Traverse right, then down, then left, then up, adjusting boundaries inwards after each traversal direction until boundaries cross.
Example answer:
Initialize boundaries top=0, bottom=m-1, left=0, right=n-1. While top <= bottom and left <= right, traverse layer by layer, updating boundaries.
13. Longest Palindromic Substring
Why you might get asked this:
A common dynamic programming or string algorithm problem testing pattern recognition and optimization.
How to answer:
Iterate through each character as a potential center of a palindrome (for odd and even lengths) and expand outwards to find the longest palindrome centered there. Keep track of the overall longest.
Example answer:
For each index i, expand around i (odd length center) and i, i+1 (even length center). Keep track of start and end indices of the longest found so far.
14. Implement strstr (Substring Search)
Why you might get asked this:
Tests basic string matching algorithms (naive approach) or more advanced pattern matching (KMP, Rabin-Karp).
How to answer:
Implement a naive nested loop approach (check if substring matches starting at each index of the main string) or explain/implement KMP for better performance.
Example answer:
Outer loop i from 0 to n-m. Inner loop j from 0 to m-1. If haystack[i+j] != needle[j], break inner loop. If inner loop completes, return i.
15. Stock Buy and Sell for Maximum Profit
Why you might get asked this:
A simple greedy algorithm or dynamic programming problem testing tracking minimums/maximums over time.
How to answer:
Iterate through the prices, keeping track of the minimum price seen so far and calculating the maximum profit possible at the current price using that minimum.
Example answer:
Initialize minprice = infinity, maxprofit = 0. Loop through prices: minprice = min(minprice, currentprice), maxprofit = max(maxprofit, currentprice - min_price).
16. Intersection Point in Y Shaped Linked Lists
Why you might get asked this:
Tests linked list manipulation, understanding of different list lengths, and finding common nodes.
How to answer:
Calculate the lengths of both lists. Move the pointer of the longer list ahead by the difference in lengths. Then traverse both lists simultaneously until pointers meet, which is the intersection point.
Example answer:
Find lengths L1, L2. Move pointer of longer list abs(L1-L2) steps forward. Traverse both lists simultaneously step by step; first common node is intersection.
17. Detect and Remove Loop in Linked List
Why you might get asked this:
Combines cycle detection with the logic to find the start of the cycle and break the link.
How to answer:
First, detect the loop using slow/fast pointers. If a loop exists, keep one pointer at the meeting point and move the other from the head. Where they meet is the loop start. Traverse from the loop start to find the node before it and break the link.
Example answer:
Detect loop with slow/fast. If loop exists, reset slow to head. Move slow and fast (from meeting point) one step at a time. They meet at loop start. Traverse from loop start to find node before it and set its next to null.
18. Trapping Rain Water
Why you might get asked this:
A challenging array problem testing understanding of boundaries, finding maximums, and calculating areas based on profiles.
How to answer:
For each bar, calculate the amount of water above it. This is determined by the minimum of the maximum height to its left and the maximum height to its right, minus the current bar's height. Sum water for all bars.
Example answer:
Precompute maxleft[i] and maxright[i] arrays. Iterate from i=1 to n-2: water[i] = max(0, min(maxleft[i], maxright[i]) - height[i]). Sum water[i].
19. Count Inversions in Array
Why you might get asked this:
Tests understanding of sorting algorithms (specifically Merge Sort) and using modifications to count pairs meeting a condition.
How to answer:
Modify the Merge Sort algorithm. During the merge step, if an element from the right subarray is smaller than an element from the left subarray, it signifies inversions involving the remaining elements in the left subarray.
Example answer:
Use a recursive merge sort function. In the merge step, when copying arr[j] (from right) before arr[i] (from left), increment inversion count by mid - i + 1.
20. Chocolate Distribution Problem
Why you might get asked this:
Tests sorting and sliding window techniques for optimizing a selection process based on minimum difference.
How to answer:
Sort the array of packet sizes. Use a sliding window of size M (number of students) to find the minimum difference between the maximum and minimum values within that window.
Example answer:
Sort the array of chocolate packets. Iterate from i = 0 to n-m. Calculate difference arr[i+m-1] - arr[i]. Keep track of the minimum difference found.
21. Check if Palindrome
Why you might get asked this:
A basic string or list problem testing two-pointer or iterative comparison techniques.
How to answer:
Use two pointers, one starting from the beginning and the other from the end. Move them inwards, comparing characters at each step. If all characters match until pointers meet or cross, it's a palindrome.
Example answer:
Initialize left=0, right=length-1. While left < right, if s[left] != s[right], return false. Increment left, decrement right. If loop finishes, return true.
22. Permutations of a String
Why you might get asked this:
Tests understanding of recursion and backtracking for generating combinations or arrangements.
How to answer:
Use a recursive backtracking function. For each position, try placing every unused character there. Mark the character as used and recurse for the next position. Backtrack by unmarking and removing the character.
Example answer:
Recursive function permute(currentstring, remainingchars): if remainingchars is empty, add currentstring to results. Else, loop through remainingchars, append char to currentstring, remove char from remaining_chars, call permute recursively.
23. Reverse Words in a String
Why you might get asked this:
Tests string splitting, array/list reversal, and joining techniques.
How to answer:
Split the string into an array of words using spaces as delimiters. Reverse the order of words in the array. Join the words back into a string with spaces. Handle multiple spaces.
Example answer:
Trim leading/trailing spaces. Split string by spaces (handling multiple spaces). Reverse the resulting array of words. Join the words with a single space.
24. Find Middle Element of Linked List
Why you might get asked this:
Tests linked list traversal and the ability to use multiple pointers for relative movement.
How to answer:
Use two pointers: a slow pointer that moves one step at a time, and a fast pointer that moves two steps at a time. When the fast pointer reaches the end of the list, the slow pointer will be at the middle.
Example answer:
Initialize slow = head, fast = head. While fast and fast.next are not null, move slow = slow.next and fast = fast.next.next. Return slow.
25. Merge Intervals
Why you might get asked this:
Evaluates sorting and interval management logic, a common pattern in scheduling or range problems.
How to answer:
Sort the intervals based on their start times. Iterate through the sorted intervals, merging the current interval with the previous one if they overlap. If they don't overlap, add the previous merged interval to the result and start a new merged interval with the current one.
Example answer:
Sort intervals by start time. Iterate. If current interval starts before or at end of last merged interval, update end of last merged to max(lastend, currentend). Else, add current to result list.
26. Balanced Parentheses
Why you might get asked this:
A classic stack-based problem testing structure validation and matching opening/closing elements.
How to answer:
Use a stack. Iterate through the string. Push opening brackets onto the stack. When a closing bracket is encountered, check if the stack is empty or if the top of the stack is the corresponding opening bracket. Pop if it matches; otherwise, it's unbalanced. The string is balanced if the stack is empty at the end.
Example answer:
Use a stack. Map closing brackets to opening ones. Loop through string: if open, push. If close, check stack top; pop if match, else invalid. After loop, balanced if stack is empty.
27. Convert Roman Number to Integer
Why you might get asked this:
Tests string parsing and understanding of numerical systems with special rules (like subtraction for IV, IX).
How to answer:
Iterate through the Roman numeral string from right to left. Maintain a running sum. If the current symbol's value is less than the previous symbol's value, subtract it; otherwise, add it.
Example answer:
Map Roman chars to values. Iterate right to left. If current value < previous value, subtract current. Else, add current. Keep track of previous value.
28. Implement Queue using Stacks
Why you might get asked this:
Tests understanding of abstract data types and how to simulate one using the operations of another.
How to answer:
Use two stacks: inputstack for enqueue and outputstack for dequeue. To enqueue, push onto inputstack. To dequeue, if outputstack is empty, pop all elements from inputstack and push them onto outputstack. Then pop from output_stack.
Example answer:
Enqueue: Push element onto inputstack. Dequeue: If outputstack is empty, move all elements from inputstack to outputstack. Pop from output_stack.
29. Find All Anagrams in a String
Why you might get asked this:
Evaluates understanding of string properties, character frequency mapping, and sliding window techniques.
How to answer:
Use a sliding window of size equal to the pattern length. Maintain frequency maps (or arrays) for the pattern and the current window. Slide the window one character at a time, updating frequency maps, and check if the window's map matches the pattern's map.
Example answer:
Use frequency arrays for pattern p and window in string s. Slide window of size p.length() across s. At each step, update window frequency. If window frequency matches pattern frequency, record window start index.
30. Kth Smallest Element in an Array
Why you might get asked this:
Similar to K-th Largest, this tests sorting, selection algorithms (Quickselect), or min/max heap usage.
How to answer:
Sort the array and return the element at index k-1. Alternatively, use a max-heap of size K to keep track of the K smallest elements seen so far, or use Quickselect (average O(n)).
Example answer:
Sort the array in ascending order. The element at index k-1 is the K-th smallest. For {7,10,4,3,20,15}, k=3, sorted {3,4,7,10,15,20}, result is 7.
Other Tips to Prepare for a machine coding round questions
Preparation is key to acing machine coding round questions. Don't just memorize solutions; understand the underlying algorithms and data structures. Practice implementing problems from scratch, focusing on writing clean, readable, and efficient code. Pay close attention to edge cases and constraint handling. Test your code thoroughly with various inputs. As the legendary computer scientist Edsger Dijkstra said, "The most important single aspect of software development is reliability." Ensure your code is robust. Consider using tools like Verve AI Interview Copilot to practice explaining your thought process and code, which is often part of the evaluation in machine coding round questions. Verve AI Interview Copilot at https://vervecopilot.com can provide feedback on your approach and communication style. Familiarize yourself with common libraries and language features in your preferred programming language. Practice writing functions and classes that are well-structured. Remember, "The code you write today is the legacy you leave tomorrow," so strive for quality even under pressure. Utilizing resources like Verve AI Interview Copilot can give you an edge by simulating the interview environment for machine coding round questions.
Frequently Asked Questions
Q1: What language should I use for machine coding round questions?
A1: Use a language you are most comfortable and proficient in, like Python, Java, C++, or JavaScript.
Q2: How important are test cases in a machine coding round?
A2: Crucial. You should write test cases yourself to demonstrate robust code handling edge cases.
Q3: Should I optimize for time or space complexity first?
A3: Generally, aim for correctness first, then optimize for time, and finally for space, discussing trade-offs.
Q4: Is it okay to ask questions during the round?
A4: Absolutely, ask clarifying questions if the problem statement is unclear. It shows engagement.
Q5: What if I get stuck on a problem?
A5: Articulate your thought process, explain where you're stuck, and discuss potential approaches.
Q6: How is the coding style evaluated?
A6: Evaluators look for readability, clarity, consistency, meaningful variable names, and proper indentation.
