LeetCode/cs/longest-strictly-increasing-or-strictly-decreasing-subarray.cs

public class Solution {
    private record MonotonicAcc(int Increasing, int Decreasing, int Max) {
        public MonotonicAcc() : this(1, 1, 1) { }

        public MonotonicAcc Increase() => new(Increasing + 1, 1, Math.Max(Max, Increasing + 1));
        public MonotonicAcc Decrease() => new(1, Decreasing + 1, Math.Max(Max, Decreasing + 1));
        public MonotonicAcc Reset() => new(1, 1, Max);
    }

    public int LongestMonotonicSubarray(int[] nums) =>
        nums.Zip(nums.Skip(1)).Aggregate(
            new MonotonicAcc(),
            (acc, pair) => pair switch {
                _ when pair.First < pair.Second => acc.Increase(),
                _ when pair.First > pair.Second => acc.Decrease(),
                _ => acc.Reset(),
            }
        ).Max;

}