1. 题目
2. 分析
这题的官方题解给出了一个深搜版本的代码，值得学习。
3. 代码
class Solution:def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:# 记录每门课程的入度in_degree = [0] * numCoursesc2c = defaultdict(list)for i in range(len(prerequisites)):a,b = prerequisites[i]in_degree[a] += 1c2c[b].append(a)cnt = 0 # 已经上过的课while(True):# 找出一门课程，它的入度为0，可以先学习，并释放依赖cur_learn = 0while(cur_learn < numCourses):if in_degree[cur_learn] == 0:cnt+=1in_degree[cur_learn] = -1 # 置标签breakcur_learn += 1if cur_learn == numCourses:breakfor i in c2c[cur_learn]:if in_degree[i] > 0:in_degree[i] -= 1if cnt == numCourses:return Truereturn False
