Ironically, it helps to think of the HR screening process as a really dumb algorithm. The HR staffer likely has little to no understanding of how to ferret out "knowledge of algorithms," (or any other job skill, for that matter). So he defaults to a list of keywords or phrases -- interpreted very literally -- from a job description received from the hiring manager.
His internal logic is pretty much driven by two directives:
1: If a keyword or phrase is in the job description, a successful applicant MUST have it on his resume. (Word for word, preferably).
2: Anything on a candidate's resume that is not on the job description is irrelevant.
In fairness, there is some legitimate value to the HR screening process. It is a filter. A dumb filter, but a filter that the hiring manager doesn't have time to run on X hundred (or Y thousand) resumes. Some HR filters are designed to screen out resumes that don't contain the right keywords. Others are designed to select for resumes that match all the right keywords. Either way, the effect is similar. Of course, such a process can (and does) weed out a lot of very talented, very qualified people.
The trick is learning how to game the filter. The filter penalizes creative or unusual word choices. The filter flags candidates who reference someone they've met or spoken to at the company (doubly so if that person is the actual referrer). The filter rewards fidelity to the letter of the job description. Tailor your cover letter and resume accordingly.