<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:
    int numberOfSubarrays(vector<int>& a, int k) {
        int l = 1, r = 1;
        int oddCount = 1;
        int count = 0;

        vector<int> oddIndex;
        oddIndex.push_back(-1);

        for(int i = 0; i<a.size(); i++) {
            if(a[i]&1)
                oddIndex.push_back(i);
        }

        oddIndex.push_back(a.size());

        // cout<<(oddIndex.size()-k+2<0);
        if(oddIndex.size() - k + 2 < 0)
            return 0;
            

        // for(int i = 0; i<oddIndex.size(); i++) {
        //     cout<<oddIndex[i]<<" ";
        // }

        // cout<<endl;

        while(r<oddIndex.size()-1) {
            if(oddCount == k) {
                // cout<<(oddIndex[l] - oddIndex[l-1]) * (oddIndex[r+1] - oddIndex[r])<<" ";
                count+=(oddIndex[l] - oddIndex[l-1]) * (oddIndex[r+1] - oddIndex[r]);
                l++;
                r++;
            }

            else {
                oddCount++;
                r++;
            }
        }
        cout<<endl;
        return count;
    }
};
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