Input: piles = [30,11,23,4,20], h = 5
Explanation: With h=5, and 5 piles, Koko must eat each pile in exactly one hour. To do this, her speed 'k' must be at least the size of the largest pile. max(piles) is 30. So, k=30 ensures each pile is eaten in 1 hour (e.g., ceil(30/30)=1, ceil(11/30)=1, etc.), total 5 hours. Any k < 30 (e.g., k=29 for pile 30) would take 2 hours for that pile, exceeding total hours.