← Walmart Labs Interview Insights
I've seen this question a dozen times and still fumbled the merge step a bit under pressure.
Start by clarifying the problem and constraints, then explain the divide-and-conquer strategy of merge sort. Walk through the implementation step-by-step, covering the merge function and recursion, and analyze time/space complexity. Finally, discuss optimizations and edge cases.
Pro tip: Mention that merge sort is stable and often used for external sorting due to its sequential access pattern, which is relevant for large-scale systems like Walmart Labs. Also, be prepared to discuss iterative vs recursive implementations and trade-offs.
Ask about input size, data types, memory constraints, and whether stability is required. This shows you consider practical aspects before coding.
Describe the divide-and-conquer approach: recursively split the array into halves until single elements, then merge sorted halves. Emphasize the merge step as the core operation.
Write a helper function that takes two sorted subarrays and merges them into a single sorted array. Use temporary arrays or in-place merging with pointers.
Write the recursive function that splits the array and calls merge. Handle base cases (array of size 0 or 1).
State time complexity O(n log n) and space complexity O(n). Mention optimizations like using insertion sort for small subarrays and avoiding unnecessary copying.
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