题目描述
现在你总共有 n 门课需要选,记为 0 到 n-1。
在选修某些课程之前需要一些先修课程。 例如,想要学习课程 0 ,你需要先完成课程 1 ,我们用一个匹配来表示他们: [0,1]
给定课程总量以及它们的先决条件,判断是否可能完成所有课程的学习?
思路
代码
from typing import List
from collections import deque
class Solution:
def canFinish(self,numCourses:int,prerequisites:List[List[int]]) ->bool:
clen = len(prerequisites)
if clen == 0:
return True
in_degrees = [0 for _ in range(numCourses)]
adj = [set() for _ in range(numCourses)]
for second, first in prerequisites:
in_degrees[second] += 1
adj[first].add(second)
queue = deque()
for i in range(numCourses):
if in_degrees[i] == 0:
queue.append(i)
counter = 0
while queue:
top = queue.popleft()
counter += 1
for successor in adj[top]:
in_degrees[successor] -= 1
if in_degrees[successor] == 0:
queue.append(successor)
return counter == numCourses