Use multi-threading when we check edges

- add openmp support
- use the thread-safe dense_bitset instead of boost::dynamic_bitset

Author: lqhl

CMakeLists.txt

@@ -16,7 +16,7 @@ endif()
 
 set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "Release" "Debug")
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -g -std=c++11 -pthread")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -g -std=c++11 -pthread -fopenmp")
 set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_EXE_LINK_FLAGS_RELEASE} -Ofast -DNDEBUG")
 
 add_subdirectory(threadpool11)