Lintcode 615. Course Schedule (Medium) Python

题目：https://www.lintcode.com/problem/course-schedule/description
思路：indgree = [[0,[]] for i in range(numCourses)]建立一个indegree数组，记录 [需要修的优先课程数，[是哪些科目的条件]]

class Solution:
    """
    @param: numCourses: a total of n courses
    @param: prerequisites: a list of prerequisite pairs
    @return: true if can finish all courses or false
    """
    def canFinish(self, numCourses, prerequisites):
        # write your code here

        if numCourses == 0 or prerequisites == None or len(prerequisites)==0:
            return True
        indgree = self.indgreeproduct(numCourses,prerequisites)
        queue = []
        hashtable = set()
        for i in range(numCourses):
            if indgree[i][0] == 0 :
                queue.append(i)
                hashtable.add(i)        
        while queue:
            current = queue.pop(0)
            for i in indgree[current][1]:
                indgree[i][0] -= 1
                if indgree[i][0] == 0:
                    queue.append(i)
                    hashtable.add(i)    
        if len(hashtable) == numCourses:
            return True 
        return False
            
    def indgreeproduct(self,numCourses, prerequisites):
        indgree = [[0,[]] for i in range(numCourses)]
        for i in prerequisites:
            if i[1] not in indgree[i[0]][1]:
               indgree[i[1]][0] += 1 
               indgree[i[0]][1].append(i[1])
        return indgree