"""
207. Course Schedule
Difficulty: Medium
https://leetcode.com/problems/course-schedule/

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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] = [ai, bi] indicates that you must take course bi
first if you want to take course ai.

• 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 <= ai, bi < numCourses

        • All the pairs prerequisites[i] are unique.
"""


class Solution:
    def canFinish(self, numCourses: int, prerequisites: list[list[int]]) -> bool:
        indegree = [0] * numCourses
        adj = [[] for x in range(numCourses)]
        for prereq in prerequisites:
            adj[prereq[1]].append(prereq[0])
            indegree[prereq[0]] += 1

        queue = []

        for i in range(numCourses):
            if indegree[i] == 0:
                queue.append(i)

        visited = 0
        while queue:
            node = queue.pop(0)
            visited += 1
            for neighbor in adj[node]:
                indegree[neighbor] -= 1
                if indegree[neighbor] == 0:
                    queue.append(neighbor)

        return numCourses == visited