Question: http://www.lintcode.com/en/problem/course-schedule-ii/ There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair:

Question: http://www.lintcode.com/en/problem/topological-sorting/ Given an directed graph, a topological order of the graph nodes is defined as follow: For each directed edge A -> B in graph, A must before B in the order list. The first node in the order can be any node