Read integers from coupled lines in a text file
You're turning the whole input file into a vector of vectors. That's fine, but you state yourself that your input has structure. It would be nice to have that structure reflected in your program:


since the lines are couple in pairs I'd like to see a code block that clearly processes a pair of lines
you should then eliminate the redundancy that the second number of the 1 st line equals the number of items on the second.