# Minimum Number of K Consecutive Bit Flips in C++

Suppose we have an array A. This is containing only 0s and 1s, here a K-bit flip consists of choosing a (contiguous) subarray of length K and simultaneously inverting the bits n the subarray. We have to find the minimum number of K-bit flips required so that there is no 0 in the array. If there is no such possibility, then return -1.

So, if the input is like [0,0,0,1,0,1,1,0] and K = 3, then the output will be 3, as we need to perform the operations three times, on the first try flip A to A, the array will be [1,1,1,1,0,1,1,0], on the second run flip A to A, the array will be [1,1,1,1,1,0,0,0], and in the 3rd move change A to A, the array will be [1,1,1,1,1,1,1,1].

To solve this, we will follow these steps −

• n := size of A

• Define an array moves of size n

• counter := 0

• for initialize i := 0, when i + K <= n, update (increase i by 1), do −

• if i > 0, then −

• moves[i] := moves[i] + moves[i - 1]

• if not ((moves[i] mod 2) + A[i]) mod 2 is non-zero, then −

• moves[i] := moves[i] + 1

• if i + K < n, then −

• moves[i + K] - = 1

• (increase counter by 1)

• for i < n, update (increase i by 1), do −

• if i > 0, then −

• moves[i] := moves[i] + moves[i - 1]

• if not ((moves[i] mod 2) + A[i]) mod 2 is non-zero, then −

• return -1

• return counter

Let us see the following implementation to get better understanding −

## Output

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
int minKBitFlips(vector<int>& A, int K){
int n = A.size();
vector<int> moves(n);
int i;
int counter = 0;
for (i = 0; i + K <= n; i++) {
if (i > 0)
moves[i] += moves[i - 1];
if (!(((moves[i] % 2) + A[i]) % 2)) {
moves[i] += 1;
if (i + K < n)
moves[i + K] -= 1;
counter++;
}
}
for (; i < n; i++) {
if (i > 0)
moves[i] += moves[i - 1];
if (!(((moves[i] % 2) + A[i]) % 2))
return -1;
}
return counter;
}
};
main(){
Solution ob;
vector<int> v = {0,0,0,1,0,1,1,0};
cout << (ob.minKBitFlips(v, 3));
}

## Input

{0,0,0,1,0,1,1,0}, 3

## Output

3

Updated on: 04-Jun-2020

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