Minimum Number of K Consecutive Bit Flips

Problem Description

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[0], then flip nums[2].

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[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]

Constraints:

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

Solution (JavaScript)

/**
 * @param {number[]} A
 * @param {number} K
 * @return {number}
 */
var minKBitFlips = function(A, K) {
    const len = A.length;
    const a = Array(len).fill(0);
    let ans = 0, flip = 0;
    
    for(let i = 0; i < len; i++){
        flip ^= a[i];
        if(A[i] === flip){
            ans++;
            if(i + K > len) return -1;
            flip ^= 1;
            if(i + K < len) a[i+K] ^= 1;
        }
    }
    
    return ans;
};