prerequisites.py

from collections import defaultdict, deque
from typing import List


def prerequisites(n: int, prerequisites: List[List[int]]) -> bool:
    graph = defaultdict(list)
    in_degrees = [0] * n
    # Represent the graph as an adjacency list and record the in-
    # degree of each course.
    for prerequisite, course in prerequisites:
        graph[prerequisite].append(course)
        in_degrees[course] += 1
    queue = deque()
    # Add all courses with an in-degree of 0 to the queue.
    for i in range(n):
        if in_degrees[i] == 0:
            queue.append(i)
    enrolled_courses = 0
    # Perform topological sort.
    while queue:
        node = queue.popleft()
        enrolled_courses += 1
        for neighbor in graph[node]:
            in_degrees[neighbor] -= 1
            # If the in-degree of a neighboring course becomes 0, add 
            # it to the queue.
            if in_degrees[neighbor] == 0:
                queue.append(neighbor)
    # Return true if we've successfully enrolled in all courses.
    return enrolled_courses == n