Palo Alto Networks·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Interviewed for a software engineer role at Palo Alto Networks and hit a LeetCode-style coding problem. Pretty standard stuff, nothing too wild.

Questions Asked (1)

Solve the classic sorted array merge problem: given two sorted integer arrays, merge the second into the first in-place.

Algorithms & Data Structures

Author's notes

LeetCode 88.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints, especially that the first array has enough space to hold the merged result. Then propose an efficient in-place merge using three pointers starting from the end of both arrays to avoid overwriting. Walk through the algorithm, analyze complexity, and discuss edge cases.

Pro tip: Mention that merging from the end is optimal because it avoids shifting elements, and explicitly state that the time complexity is O(m+n) and space is O(1). This shows you understand the trade-offs and can optimize for in-place operations.

1. Clarify the problem

Confirm that the first array has sufficient capacity (m+n) and that m and n represent the number of valid elements in each array. Ask if the arrays are sorted in ascending order and if in-place means O(1) extra space.

2. Choose the right approach

Explain that merging from the end with three pointers (i, j, k) is optimal because it avoids shifting elements and uses constant extra space. Contrast with merging from the front, which would require extra space or shifting.

3. Walk through the algorithm

Initialize i = m-1, j = n-1, k = m+n-1. While i >= 0 and j >= 0, compare nums1[i] and nums2[j], place the larger at nums1[k], and decrement the corresponding pointer and k. After the loop, if any elements remain in nums2, copy them to the beginning of nums1.

4. Analyze complexity and edge cases

State that time complexity is O(m+n) and space is O(1). Discuss edge cases: one array empty, all elements of one array smaller, duplicates, and negative numbers.

5. Test with examples

Walk through a simple example like nums1 = [1,2,3,0,0,0], m=3, nums2 = [2,5,6], n=3 to demonstrate correctness. Mention that you would write unit tests for edge cases.

Key Points to Mention

In-place merge using three pointers from the end
Time complexity O(m+n) and space complexity O(1)
Avoiding overwriting by starting from the end
Handling remaining elements in nums2 after the main loop
Edge cases: empty arrays, all elements of one array smaller, duplicates
Comparison with alternative approaches (e.g., using extra space or merging from front)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.