Description
![](https://kickstart.best/wp-content/uploads/2022/05/image-20-1024x589.png)
Submission
class Solution { public: int minKBitFlips(vector<int>& nums, int k) { int n = nums.size(); vector<int> diff(n+1, 0); int sum = 0; int ret = 0; for(int i = 0; i < n; ++i) { sum += diff[i]; if((sum + nums[i]) % 2 == 1) continue; if(i > n - k) { return -1; } diff[i+k]--; sum++; ret++; } return ret; } };
![](https://kickstart.best/wp-content/uploads/2022/05/image-21-1024x447.png)