[egor83]

Strong tradition of STEM education, back from the Soviet times. Military complex was very strong in the USSR, which resulted in quality education (again, just STEM, not so in humanities) - basically, you need to know physics and maths very well to build the bomb.

I guess that applies to other Eastern bloc countries to some extent (see Polish universities at ##5, 9 and 25, Ukraine at #11, Belarus at #17).

[jakozaur]

In case of Poland it helps that algorithm competitions are popular in high school. Each year top winners get a free pass to entry any CS university. So if you SAT style exams are not your thing there is an alternative way.