#824 · #995 · Minimum Number of K Consecutive Bit Flips(K 连续位的最小翻转次数)

You are given a binary array nums and an integer k. In one operation, choose a window of length k (starting at i with i + k <= n) and flip every bit in it. Return the minimum number of operations to make every element 1, or -1 if impossible. Constraints: 1 <= nums.length <= 10^5, 1 <= k <= nums.length.