Find the Largest Rating Threshold Supported by K Instances

Given an array of integer instance ratings, return the largest integer k such that at least k instances have ratings greater than or equal to k.

Input and Output

• Input: an array of integer ratings, one value per instance.
• Output: one integer, the maximum qualifying k. Return 0 when no positive k qualifies.
• k cannot exceed the number of instances. A rating equal to k meets the threshold.
• For this practice version, an empty array has answer 0.

Example 1

ratings = [3, 0, 6, 1, 5]
answer = 3

Three ratings are at least 3: 3, 6, and 5.

Example 2

ratings = [0, 0]
answer = 0