The algorithm.sty and aglrothmic.sty files are missing from app-text/tetex-2.0.2-r1. I could not find anything in the change log to explain why.
from the ChangeLog included in the tetex-texmf-2.0.2 src: Sun May 26 15:25:42 CEST 2002 ... * algorithms package removed for license reasons ... The documentation from the texmf package is located in /usr/share/texmf, check out the ChangeLog located in there.