Max Consecutive Ones III

int longestOnes(vector<int>& A, int K) {
    int res=0;
    int f=0;
    int start=0;
    for(int i=0;i<A.size();++i) {
        f+=1-A[i];
        // If flips exceed K, slide the window forward
        while(f>K) if (A[start++]==0) --f;
        // Record the maximum
        res=max(res, i-start+1);
    }
    return res;
}