foo.cpp: In function 'void dfs(int, int)':
foo.cpp:36:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
foo.cpp: In function 'void reach(int)':
foo.cpp:46:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
foo.cpp: In function 'void rev_reach(int)':
foo.cpp:56:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
foo.cpp: In function 'int next_int()':
foo.cpp:84:23: error: 'getchar' was not declared in this scope