Ways to Split Array Into Good Subarrays
<p>You are given a binary array <code>nums</code>.</p>

<p>A subarray of an array is <strong>good</strong> if it contains <strong>exactly</strong> <strong>one</strong> element with the value <code>1</code>.</p>

<p>Return <em>an integer denoting the number of ways to split the array </em><code>nums</code><em> into <strong>good</strong> subarrays</em>. As the number may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

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

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

<pre>
<strong>Input:</strong> nums = [0,1,0,0,1]
<strong>Output:</strong> 3
<strong>Explanation:</strong> There are 3 ways to split nums into good subarrays:
- [0,1] [0,0,1]
- [0,1,0] [0,1]
- [0,1,0,0] [1]
</pre>

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

<pre>
<strong>Input:</strong> nums = [0,1,0]
<strong>Output:</strong> 1
<strong>Explanation:</strong> There is 1 way to split nums into good subarrays:
- [0,1,0]
</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>0 &lt;= nums[i] &lt;= 1</code></li>
</ul>
Array; Math; Dynamic Programming
class Solution {
public:
    int numberOfGoodSubarraySplits(vector<int>& nums) {
        const int mod = 1e9 + 7;
        int ans = 1, j = -1;
        for (int i = 0; i < nums.size(); ++i) {
            if (nums[i] == 0) {
                continue;
            }
            if (j > -1) {
                ans = 1LL * ans * (i - j) % mod;
            }
            j = i;
        }
        return j == -1 ? 0 : ans;
    }
};