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Yes, problems like Maximum Average Subarray II are common in technical interviews at FAANG and similar companies. They test understanding of advanced techniques such as binary search on answers, prefix sums, and optimization strategies for large input constraints.
Binary search is used because the maximum average lies within a numeric range between the minimum and maximum array values. Instead of checking all subarrays, we repeatedly guess an average and verify feasibility using prefix sums, narrowing the range until we reach the optimal value.
The optimal approach uses binary search on the possible average value combined with a prefix sum validation technique. By transforming the array based on the guessed average, we can efficiently check if a valid subarray of length at least k exists. This reduces the problem from brute-force enumeration to a logarithmic search over averages.
Prefix sums are the key technique used in this problem. They allow efficient computation of subarray sums and help verify whether a subarray with a non-negative transformed sum exists when testing a candidate average.