I knew it was a sliding window problem pretty quickly, the constraint of two distinct types makes that obvious.
Recognize this as the 'Fruit Into Baskets' problem, which is equivalent to finding the longest subarray with at most two distinct values. Use a sliding window with a hash map to track fruit counts, expanding the right pointer and shrinking the left when the window exceeds two types. Return the maximum window length seen.
Pro tip: Clarify edge cases upfront (empty array, single fruit type) and mention that the algorithm runs in O(n) time and O(1) space since the map holds at most three entries. This shows attention to detail and efficiency.
Confirm that you must pick from consecutive trees and can carry only two distinct fruit types. Restate the problem as finding the longest contiguous subarray with at most two distinct values.
Use a hash map to count the frequency of each fruit type in the current window, and two pointers (left and right) to represent the sliding window.
Iterate the right pointer over the array, adding fruits to the map. When the map size exceeds 2, move the left pointer forward, decrementing counts and removing fruits with zero count, until the window is valid again.
After each expansion, update the maximum length of the valid window. Continue until the right pointer reaches the end of the array.
Return the maximum length found, which represents the maximum number of fruits you can collect.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.