1574. Shortest Subarray to be Removed to Make Array Sorted

public class Solution
{
    public int FindLengthOfShortestSubarray(int[] arr)
    {
        int n = arr.Length;
        int l = 0;
        int r = n - 1;

        // arr[0..l] is non-decreasing prefix.
        while (l < n - 1 && arr[l + 1] >= arr[l])
            ++l;
        // arr[r..n - 1] is non-decreasing suffix.
        while (r > 0 && arr[r - 1] <= arr[r])
            --r;
        // Remove arr[l + 1..n - 1] or arr[0..r - 1]
        int ans = Math.Min(n - 1 - l, r);

        // Since arr[0..l] and arr[r..n - 1] are non-decreasing, we place pointers
        // at the rightmost indices, l and n - 1, and greedily shrink them toward
        // the leftmost indices, 0 and r, respectively. By removing arr[i + 1..j],
        // we ensure that `arr` becomes non-decreasing.
        int i = l;
        int j = n - 1;
        while (i >= 0 && j >= r && j > i)
        {
            if (arr[i] <= arr[j])
                --j;
            else
                --i;
            ans = Math.Min(ans, j - i);
        }

        return ans;
    }
}