anujajoseph:

If the source file is too large to fit into memory, then the second suggestion might be better. But since computers tend to have so much RAM nowadays, most files will fit into memory.

Update: On rereading the thread, I realize that in my first post I left out a word in the second suggestion. It should be an array of line numbers.

...roboticus

When your only tool is a hammer, all problems look like your thumb.