DoorDash virtual onsite question:

Asked this: https://leetcode.com/discuss/interview-question/846916/Validate-Orders-Path-(Doordash)

Follow up: Find longest valid subarray

Ex 1: orders = ['P1', 'P1', 'D1'], return ['P1', 'D1']
Ex 2: orders = ['P1', 'P1', 'D1', 'D1'], return ['P1', 'D1']

How can we solve this? I could not think of a better solution than brute force.