<p>Given an array of integers <code>nums</code> and an integer <code>k</code>. A continuous subarray is called <strong>nice</strong> if there are <code>k</code> odd numbers on it.</p>

<p>Return <em>the number of <strong>nice</strong> sub-arrays</em>.</p>

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

<pre>
<strong>Input:</strong> nums = [1,1,2,1,1], k = 3
<strong>Output:</strong> 2
<strong>Explanation:</strong> The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1].
</pre>

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

<pre>
<strong>Input:</strong> nums = [2,4,6], k = 1
<strong>Output:</strong> 0
<strong>Explanation:</strong> There are no odd numbers in the array.
</pre>

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

<pre>
<strong>Input:</strong> nums = [2,2,2,1,2,2,1,2,2,2], k = 2
<strong>Output:</strong> 16
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 50000</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10^5</code></li>
	<li><code>1 &lt;= k &lt;= nums.length</code></li>
</ul>

class Solution {
public:
    void print_vi(const vector<int> &vi) {
        cout << "{ ";
        for (int i : vi) {
            cout << i << ", ";
        }
        cout << '}' << endl;
    }
    int numberOfSubarrays(vector<int>& nums, int k) {
        int n = nums.size();
        vector<int> chunks; // space between every pair of odd numbers (separated only by evens) is a chunk

        int curEvenCt = 0;
        for (int i = 0; i < n; i++) {
            if (nums[i] % 2 == 1) {
                chunks.push_back(curEvenCt + 1);
                curEvenCt = 0;
            } else {
                curEvenCt++;
            }
        }
        chunks.push_back(curEvenCt+1);
        int ans = 0;
        for (int i = 0; i < int(chunks.size()); i++) {
            int j = i - k;
            if (j < 0) continue;
            int contrib = chunks[j] * chunks[i];
            ans += contrib;
        }
        return ans;
    }
};
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