The following is a slight update to your code, and it was Accepted at UVa Online Judge. The updated code automates the data initialization using C++ class constructors. A data_set data structure was declared whose constructor is called implicitly when an object is declared, and whose destructor is called implicitly to clean up the dynamic memory at the end of the code block in which such object is declared. Callers indexing was updated to start at index 0, and everything else is almost the same. A caller_t data structure was declared to store the caller information as a vertex in the calling circle graph. Your depth-first search aglorithm to find Strongly Connected Components SCC is correct, but the WA to your code might have been caused by incorrect array or map indexing in some boundary test case that the UVa site does not release.