View Compilation Error

0_0_5293173_21273.cpp:9:20: hash_set: No such file or directory
0_0_5293173_21273.cpp: In function `std::vector<char, std::allocator<char> > bfs(int, int, int)':
0_0_5293173_21273.cpp:49: error: `hash_set' undeclared (first use this function)
0_0_5293173_21273.cpp:49: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_5293173_21273.cpp:49: error: expected primary-expression before "int"
0_0_5293173_21273.cpp:49: error: expected `;' before "int"
0_0_5293173_21273.cpp:55: error: `sign' undeclared (first use this function)