p207.cpp

class Solution {
public:
    bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites) {
        int *indegree = (int*)malloc(sizeof(int)*numCourses);
        int *in0 = (int*)malloc(sizeof(int)*numCourses);
        int in0num = 0;
        vector<int> *out = new vector<int>[numCourses];
        int i;
        for (i = 0; i < numCourses; i++)
        {
            indegree[i] = 0;
        }
        int size = prerequisites.size();
        for (i = 0; i < size; i++)
        {
            out[prerequisites[i].first].push_back(prerequisites[i].second);
            indegree[prerequisites[i].second]++;
        }
        for (i = 0; i < numCourses; i++)
        {
            if (indegree[i] == 0)
            {
                in0[in0num++] = i;
            }
        }
        while (in0num > 0)
        {
            numCourses--;
            int c = in0[--in0num];
            size = out[c].size();
            for (i = 0; i < size; i++)
            {
                indegree[out[c][i]]--;
                if (indegree[out[c][i]] == 0)
                {
                    in0[in0num++] = out[c][i];
                }
            }
        }
        return numCourses == 0;
    }
};