<p>You are given a binary array <code>nums</code> and an integer <code>k</code>.</p>

<p>A <strong>k-bit flip</strong> is choosing a <strong>subarray</strong> of length <code>k</code> from <code>nums</code> and simultaneously changing every <code>0</code> in the subarray to <code>1</code>, and every <code>1</code> in the subarray to <code>0</code>.</p>

<p>Return <em>the minimum number of <strong>k-bit flips</strong> required so that there is no </em><code>0</code><em> in the array</em>. If it is not possible, return <code>-1</code>.</p>

<p>A <strong>subarray</strong> is a <strong>contiguous</strong> part of an array.</p>

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

<pre>
<strong>Input:</strong> nums = [0,1,0], k = 1
<strong>Output:</strong> 2
<strong>Explanation:</strong> Flip nums[0], then flip nums[2].
</pre>

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

<pre>
<strong>Input:</strong> nums = [1,1,0], k = 2
<strong>Output:</strong> -1
<strong>Explanation:</strong> No matter how we flip subarrays of size 2, we cannot make the array become [1,1,1].
</pre>

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

<pre>
<strong>Input:</strong> nums = [0,0,0,1,0,1,1,0], k = 3
<strong>Output:</strong> 3
<strong>Explanation:</strong> 
Flip nums[0],nums[1],nums[2]: nums becomes [1,1,1,1,0,1,1,0]
Flip nums[4],nums[5],nums[6]: nums becomes [1,1,1,1,1,0,0,0]
Flip nums[5],nums[6],nums[7]: nums becomes [1,1,1,1,1,1,1,1]
</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>1 &lt;= k &lt;= nums.length</code></li>
</ul>

// #include <bits/stdc++.h>
// using namespace std;
// class Solution
// {
// public:
//     int minKBitFlips(vector<int> &nums, int k)
//     {
//         int n = nums.size();
//         int ans = 0;
//         int cnt0 = 0;
//         for (int i = 0; i < n; i++)
//         {
//             if (nums[i] == 0)
//                 cnt0++;
//         }
//         if (cnt0 < k)
//         {
//             return -1;
//         }
//         for (int i = 0; i < n; i++)
//         {
//             if (nums[i] == 0)
//             {
//                 for (int j = 0; j < k; j++)
//                 {
//                     int t = i;
//                     if (nums[t] == 0)
//                     {
//                         nums[t] = 1;
//                     }
//                     else
//                     {
//                         nums[t] = 0;
//                     }
//                     t++;
//                 }
//                 ans++;
//             }
//             else
//             {
//                 continue;
//             }
//         }
//         if (ans == 0)
//         {
//             return -1;
//         }
//         return ans;
//     }
// };



class Solution
{
public:
    int minKBitFlips(vector<int> &nums, int k)
    {
        int flips = 0,ans = 0, n = nums.size();
        for(int i=0;i<n;i++){
            if(i>=k&&nums[i-k]==99){
                flips--;
            }
            if(nums[i]==(flips&1)){
                if(i+k>n){
                    return -1;
                }
                flips++;
                nums[i] = 99;
                ans++;
            }
        }   
        return ans;
    }    
};
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