Instead of keeping track of the 1s, it might be more intuitive to follow the zeros.

Here's one way to do this.

static int findLength(const vector<int> &arr, int k)
    {
      int maxLength = 0, start = 0, tempK = 0;
      
      for(int end = 0; end < arr.size(); end++){
        if(arr[end] == 0)
          tempK++;

        // If there are too many zeros, increment start
        while(tempK > k){
          if(arr[start++] == 0)
            tempK --;
        }

        maxLength = max(maxLength, end - start + 1);
      }
      return maxLength;
    }

Anyone else approach the problem like this?