Leetcode 210. Course Schedule II (topological sequencing-finding the presence of loops in a graph)

and Leetcode 207. Course Schedule (Topological ordering-finding the presence of loops in a graph) is similar.

Notice that the parallel or self-loops that may appear in the input are p:prerequistites in the for (auto).

Code:

Class solution {public:vector<int> FindOrder (int numcourses, vector<pair<int, int>>& Prerequisi TES) {//[0, {1, 2, 3}], means after finishing #0, "might" being able to take #1, #2, #3//That's, you must    Finish #0, before trying to take #1, #2, #3 map<int, vector<int>> course_chain;    Vector<int> In_degree (numcourses, 0);    Queue<int> Q;    vector<int> ret;        for (auto p:prerequisites) {//Self-loop, return empty vector.    if (P.first = = P.second) {return vector<int> (); }//No duplicate edges input if (find (Course_chain[p.second].begin (), Course_chain[p.second].end (), p.first) = = Cou    Rse_chain[p.second].end ()) {course_chain[p.second].push_back (P.first);    + + In_degree[p.first];    }} for (size_t i = 0; i < numcourses; + + i) {if (in_degree[i] = = 0) {Q.push (i);    }} for (;!q.empty (); Q.pop ()) {int pre_course = Q.front (); Ret.puSh_back (Pre_course);    for (Auto it = Course_chain[pre_course].begin (); It! = Course_chain[pre_course].end (); + + it) {--in_degree[*it];    if (in_degree[*it] = = 0) {Q.push (*it); }}} return Ret.size () ==numcourses?    Ret:vector<int> (); }};

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Leetcode 210. Course Schedule II (topological sequencing-finding the presence of loops in a graph)