Find Ideal Days

Problem Overview

• Task: Given rainfall array day and integer k, find all indices i where the prior k days are non-increasing and the following k days are non-decreasing.
• Input/Output: Input is day and k; return the ideal days in ascending order (days correspond to 1-based dates).
• Context: Alexa feature to suggest camping days from weather forecasts.
• Constraints: 1 ≤ k ≤ n ≤ 2e5, 0 ≤ day[i] ≤ 1e9; at least one ideal day exists.
• Source: Amazon interviews; a coding interview problem and interview question.