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LeetCode 1838 Frequency of the Most Frequent Element is asked at Google and Amazon. Sort, then slide a window where total cost to lift everything to the rightmost value is at most k.
LeetCode 1658 Minimum Operations to Reduce X to Zero is asked at Amazon, Google, and Meta. Reframe to longest subarray summing to total minus x for an O(n) solution.
LeetCode 845 Longest Mountain in Array is asked at Google, Amazon, and Bloomberg. Find the longest strictly increasing-then-decreasing subarray in O(n) time, O(1) space.
LeetCode 978 Longest Turbulent Subarray is asked at Google and Amazon. Track alternating comparison signs in a single O(n) pass with O(1) extra space.
LeetCode 992 Subarrays with K Different Integers is a Google, Amazon, and Meta hard. Solve in O(n) using the atMost(K) minus atMost(K-1) decomposition.