THE SMART TRICK OF 12345ASDF THAT NOBODY IS DISCUSSING

We look for the place p of each and every character in the enter within a string S wherever the keyboard rows are interleaved: the 1st 4 characters are '1QAZ' (very first column on the keyboard), another 4 figures are '2WSX' (2nd column in the keyboard) and so on. Unused positions are padded with underscores and the final ones are simply discarded.