implementation6 codeforces4 enumeration3 binary-search2 hugo2 ncpc2 ptc2 setup2 apcs1 bfs1 educational-round1 etutor1 greedy1 gym1 itsa1 linux1 mac1 math1 observation1 pc21 physics1 poj1 stack1 two-pointer1 union-find1 uva1 zerojudge1