Minimum Number of K Consecutive Bit Flips

Description

In an array A containing only 0s and 1s, a K-bit flip consists of choosing a (contiguous) subarray of length K 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.

 

Example 1:

Input: A = [0,1,0], K = 1
Output: 2
Explanation: Flip A[0], then flip A[2].

Example 2:

Input: A = [1,1,0], K = 2
Output: -1
Explanation: No matter how we flip subarrays of size 2, we can't make the array become [1,1,1].

Example 3:

Input: A = [0,0,0,1,0,1,1,0], K = 3
Output: 3
Explanation:
Flip A[0],A[1],A[2]: A becomes [1,1,1,1,0,1,1,0]
Flip A[4],A[5],A[6]: A becomes [1,1,1,1,1,0,0,0]
Flip A[5],A[6],A[7]: A becomes [1,1,1,1,1,1,1,1]

 

Note:

1. 1 <= A.length <= 30000
2. 1 <= K <= A.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;
};