检测有向图中所有周期的最有效算法是什么？
我有一个有向图表示需要执行的作业计划,作业是节点,依赖是边缘.我需要检测此图中循环的错误情况,从而导致循环依赖.
Cabal在尝试安装pango时失败,抱怨它无法找到pkg-config.
peauters:~ $ sudo cabal install pango -v
Password:
Reading available packages...
Choosing modular solver.
Resolving dependencies...
Extracting
/Users/chris/Library/Haskell/repo-cache/hackage.haskell.org/pango/0.12.3/pango-0.12.3.tar.gz
to /tmp/pango-0.12.3-76116...
creating /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup
creating /tmp/pango-0.12.3-76116/pango-0.12.3/dist
creating /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup
/usr/bin/ghc --make /tmp/pango-0.12.3-76116/pango-0.12.3/Setup.hs -o /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup/setup -odir /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup -hidir /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup -i -i/tmp/pango-0.12.3-76116/pango-0.12.3 -package Cabal-1.14.0
[1 of 2] Compiling SetupWrapper ( /tmp/pango-0.12.3-76116/pango-0.12.3/SetupWrapper.hs, /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup/SetupWrapper.o )
[2 of 2] Compiling Main ( /tmp/pango-0.12.3-76116/pango-0.12.3/Setup.hs, /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup/Main.o )
Linking /tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup/setup ...
/tmp/pango-0.12.3-76116/pango-0.12.3/dist/setup/setup configure --verbose=2
--ghc --prefix=/Library/Haskell/$compiler/lib/$pkgid --libsubdir=
--datasubdir= --docdir=$prefix/doc --enable-library-profiling --global
--flags=new-exception --constraint=process ==1.1.0.1 --constraint=pretty
==1.1.1.0 --constraint=mtl ==2.1.1 --constraint=glib ==0.12.3.1 …