class Solution {
public:
vector<int> findOrder(int numCourses, vector<vector<int>>& prerequisites) {
vector<vector<int>> edges(numCourses);
vector<int> inDegree(numCourses, 0);
for (auto &x: prerequisites) {
inDegree[x[0]] += 1;
edges[x[1]].push_back(x[0]);
}
vector<int> res;
queue<int> q;
for (int i = 0; i < numCourses; i++)
if (inDegree[i] == 0) q.push(i);
while (!q.empty()) {
int cur = q.front();
q.pop();
res.push_back(cur);
for (auto &x: edges[cur]) {
inDegree[x] -= 1;
if (inDegree[x] == 0) q.push(x);
}
}
if (res.size() != numCourses) return {};
return res;
}
};Time Complexity: O(n)
Space: O(n)
經典的拓樸排序算法
