3234. Count the Number of Substrings With Dominant Ones

public class Solution
{
    public int NumberOfSubstrings(string s)
    {
        int ans = 0;

        // Iterate through all possible number of 0s.
        for (int zero = 0; zero + zero * zero <= s.Length; ++zero)
        {
            int lastInvalidPos = -1;
            int[] count = new int[2];
            for (int l = 0, r = 0; r < s.Length; ++r)
            {
                count[s[r] - '0']++;
                // Try to shrink the window to maintain the "minimum" length of the
                // valid substring.
                for (; l < r; ++l)
                {
                    if (s[l] == '0' && count[0] > zero)
                    {
                        count[0]--; // Remove an extra '0'.
                        lastInvalidPos = l;
                    }
                    else if (s[l] == '1' && count[1] - 1 >= zero * zero)
                        count[1]--; // Remove an extra '1'.
                    else
                        break; // Cannot remove more characters.
                }
                if (count[0] == zero && count[1] >= zero * zero)
                    // Add valid substrings ending in s[r] to the answer. They are
                    // s[lastInvalidPos + 1..r], s[lastInvalidPos + 2..r], ..., s[l..r].
                    ans += l - lastInvalidPos;
            }
        }

        return ans;
    }
}