[LeetCode] 0207. Course schedule

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Medium

There are a total of numCourses courses you have to take, labeled from 0 to numCourses-1.You are given an array prerequisites where prerequisites[i] = [a _i , b _i ] indicates that you must take course b _i first if you want to take course artificial _intelligence.

For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.

Return true if you can finish all courses. Otherwise, return false.

Example 1:

Input: numCourses = 2, prerequisites = [[1,0]]
Output: true
Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.

Example 2:

Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
Output: false
Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.

Constraints:

1 <= numCourses <= 2000
0 <= prerequisites.length <= 5000
prerequisites[i].length == 2
0 <= a _i , b _i < numCourses
All the pairs prerequisites[i] are unique.

Python

				
					from collections import deque from typing import List class Solution: def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool: indegree = [0] * numCourses adj = [[] for _ in range (numCourses)] for prerequisite in prerequisites: adj[prerequisite[1]].append(prerequisite[0]) indegree[prerequisite[0]] += 1 queue = deque() for i in range(numCourses): if indegree[ i] == 0: queue.append(i) nodeVisited = 0 while queue: node = queue.popleft() nodeVisited += 1 for neighbor in adj[node]: indegree[neighbor] -= 1 if indegree[neighbor] = = 0: queue.append(neighbor) return nodeVisited == numCourses

Medium

Python

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