foo.cpp: In function 'int dfs(int, int)':
foo.cpp:32:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 for( i = 0 ; i < linker[ pos ].size() ; i++ )
                                     ^
foo.cpp: In function 'int main()':
foo.cpp:71:17: error: 'system' was not declared in this scope
 system( "pause" );
                 ^