python-leetcode-课程表

207. 课程表 - 力扣（LeetCode）

from collections import deque
class Solution:
    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
        # 构建邻接表 & 计算入度
        graph = {i: [] for i in range(numCourses)}
        in_degree = [0] * numCourses

        for a, b in prerequisites:
            graph[b].append(a)
            in_degree[a] += 1  # 计算入度
        
        # 将入度为 0 的课程加入队列
        queue = deque([i for i in range(numCourses) if in_degree[i] == 0])
        count = 0  # 统计已完成课程数

        while queue:
            curr = queue.popleft()
            count += 1  # 完成该课程
            for next_course in graph[curr]:
                in_degree[next_course] -= 1  # 减少后续课程的入度
                if in_degree[next_course] == 0:
                    queue.append(next_course)  # 继续学习入度为 0 的课程
        
        return count == numCourses  # 如果所有课程都能完成，则返回 True