标签：number ota ++ cto false which ack www etc
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: [0,1]
Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?
For example:
2, [[1,0]]
There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.
2, [[1,0],[0,1]]
There are a total of 2 courses to take. To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.
Note:
The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more about how a graph is represented.
本题最终转化为求有向图中是否有存在环，转化为拓扑序问题
class Solution { public: bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites) { vector<vector<int>> graph(numCourses); vector<int> in_degree(numCourses, 0); for (auto p : prerequisites) { graph[p.second].push_back(p.first); in_degree[p.first]++; } queue<int> q; int cnt = 0; for (int i = 0; i < numCourses; i++) { if (in_degree[i] == 0) q.push(i); } while (!q.empty()) { int cur = q.front(); q.pop(); for (auto it = graph[cur].begin(); it != graph[cur].end(); it++) { if (--in_degree[*it] == 0) q.push(*it); } } for (int i = 0; i < numCourses; i++) { if (in_degree[i] != 0) return false; } return true; } };
标签：number ota ++ cto false which ack www etc
原文地址：http://www.cnblogs.com/wxquare/p/6105456.html
