class MyNode:
    def __init__(self):
        self.out_nodes = []
        self.in_degree = 0
    
    def add_outnode(self, node):
        self.out_nodes.append(node)        
        
        
class Solution:
    def findOrder(self, numCourses, prerequisites):
        """
        :type numCourses: int
        :type prerequisites: List[List[int]]
        :rtype: List[int]
        """
        node_map = {}
        for course in range(numCourses):
            node_map[course] = MyNode()
        for reqs in prerequisites:            
            end_node = node_map[reqs[0]]
            start_node = node_map[reqs[1]]
            start_node.add_outnode(end_node)
            end_node.in_degree += 1
            
        leaves = [node for node in node_map.values() if node.in_degree == 0]
                
        order = []        
        while leaves:
            leaf = leaves.pop()
            order.append(leaf)
            for out_node in leaf.out_nodes:
                out_node.in_degree -= 1
                if out_node.in_degree == 0:
                    leaves.append(out_node)
        return order