Number of Zero-Filled Subarrays
<p>Given an integer array <code>nums</code>, return <em>the number of <strong>subarrays</strong> filled with </em><code>0</code>.</p>

<p>A <strong>subarray</strong> is a contiguous non-empty sequence of elements within an array.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,3,0,0,2,0,0,4]
<strong>Output:</strong> 6
<strong>Explanation:</strong> 
There are 4 occurrences of [0] as a subarray.
There are 2 occurrences of [0,0] as a subarray.
There is no occurrence of a subarray with a size more than 2 filled with 0. Therefore, we return 6.</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [0,0,0,2,0,0]
<strong>Output:</strong> 9
<strong>Explanation:
</strong>There are 5 occurrences of [0] as a subarray.
There are 3 occurrences of [0,0] as a subarray.
There is 1 occurrence of [0,0,0] as a subarray.
There is no occurrence of a subarray with a size more than 3 filled with 0. Therefore, we return 9.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [2,10,2019]
<strong>Output:</strong> 0
<strong>Explanation:</strong> There is no subarray filled with 0. Therefore, we return 0.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-10<sup>9</sup> &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
</ul>
Array; Math
class Solution {
public:
    long long zeroFilledSubarray(vector<int>& nums) {
        long long ans = 0;
        int cnt = 0;
        for (int& v : nums) {
            cnt = v ? 0 : cnt + 1;
            ans += cnt;
        }
        return ans;
    }
};