995. Minimum Number of K Consecutive Bit Flips
Hard
1.1K
56

You are given a binary array `nums` and an integer `k`.

A k-bit flip is choosing a subarray of length `k` from `nums` and simultaneously changing every `0` in the subarray to `1`, and every `1` in the subarray to `0`.

Return the minimum number of k-bit flips required so that there is no `0` in the array. If it is not possible, return `-1`.

A subarray is a contiguous part of an array.

Example 1:

```Input: nums = [0,1,0], k = 1
Output: 2
Explanation: Flip nums, then flip nums.
```

Example 2:

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

Example 3:

```Input: nums = [0,0,0,1,0,1,1,0], k = 3
Output: 3
Explanation:
Flip nums,nums,nums: nums becomes [1,1,1,1,0,1,1,0]
Flip nums,nums,nums: nums becomes [1,1,1,1,1,0,0,0]
Flip nums,nums,nums: nums becomes [1,1,1,1,1,1,1,1]
```

Constraints:

• `1 <= nums.length <= 105`
• `1 <= k <= nums.length`
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