3191. Minimum Operations to Make Binary Array Elements Equal to One I

You are given a binary array nums.

You can do the following operation on the array any number of times (possibly zero):

• Choose any 3 consecutive elements from the array and flip all of them.

Flipping an element means changing its value from 0 to 1, and from 1 to 0.

Return the minimum number of operations required to make all elements in nums equal to 1. If it is impossible, return -1.

class Solution {
public:
    int minOperations(vector<int>& A) {
        int n = A.size(), res = 0;
        for(int i = 0; i < n - 2; i++) {
            if(A[i]) continue;
            A[i] = !A[i];
            A[i+1] = !A[i+1];
            A[i+2] = !A[i+2];
            res++;
        }
        if(A[n-1] == 0 or A[n-2] == 0) return -1;
        return res;
    }
};