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207_Course_Schedule.py
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207_Course_Schedule.py
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#!/usr/bin/python
# -*- coding: utf-8 -*-
#author : zhangdawang
#data: 2017-9-
#difficulty degree:
#problem: 207_Course_Schedule
#time_complecity:
#space_complecity:
#beats:
class Solution(object):
def canFinish(self, numCourses, prerequisites):
def dfs(prec, c):
if not c in d: return 1
if c in prec: return 0
prec.add(c)
visit.add(c)
for nextc in d[c]:
if not dfs(prec, nextc):
return 0
prec.remove(c)
return 1
#构建字典树
d = {}
for c1, c2 in prerequisites:
if c1 in d:
d[c1].append(c2)
else:
d[c1] = [c2]
visit = set()
for c in d:
prec = set()
if c in visit:
continue
if not dfs(prec, c):
return False
return True
solute = Solution()
numCourses = 2
prerequisites = [[1,0], [0,1]]
res = solute.canFinish(numCourses, prerequisites)