Euclid 's algorithm is the fastest way to find HCF , which is very effective even for large numbers , rather than the usual factorization with writing out common factors .
As an example , here is the usual method
HCF (280 ; 320 ) = ?
We decompose 320 and 280 into prime factors

280 = 2·2·2·5·7
320 = 2·2·2·2·2·2·5
Thus HCF ( 280 ; 320 ) = 2·2·2·5 = 40
Euclid 's algorithm
HCF ( 280 ; 320 ) = 40
We divide the divisor by the remainder until zero remains in the remainder