As far as diff performance go concatenating the two large files using the diff replace all syntax is faster, uses o(1) memory, o(n) time and it's only slightly

As far as diff performance go concatenating the two large files using the diff replace all syntax is faster, uses o(1) memory, o(n) time and it's only slightly space inefficient. I'd also say it might beat the OP alghorithm in performances under certain assumption (i.e large writes vs scan read performances)