leetcode997

 class Solution:
     def findJudge(self, N: int, trust: 'List[List[int]]') -> int:
         if N==1 and len(trust)==0:
             return 1
         s = list(range(1,N+1))
         d = {}
         for t in range(len(trust)):
             a1 = trust[t][0]
             a2 = trust[t][1]
             if a1 in s:
                 s.remove(a1)
             if a2 in d.keys():
                 d.update({a2:d[a2]+1})
             else:
                 d.update({a2:1})
         if len(s)==1 and s[0] in d.keys() and d[s[0]]==N-1:
             return s[0]
         else:
             return -1