town judge

app.py

# The rules:
#The town judge trusts nobody.
# Everybody (except for the town judge) trusts the town judge.

## let's look at the example: 
# we've 3 people, and there trust is been displayed like this. [[1,2], [2,3]].
# the trust simply means that 1 trust 2, and 2 trust 3.
# so 3 doesn't trust anyone that makes 3 the town judge

 #### steps to solve it.
 
 # 1. if len of trust is less than number of people - 1. we return false or -1
 # 2. how many number of people is trusting a number, if many people are trusting a number and the number is not trusting any one that makes the 
 # the number a town judge
 
 ## example on this steps: 
 ## trust = [[[1,3], [1,4], [2,3], [2,4], [4,3]]
 ## and the number of people is 4
 ## we need to create two arrays. number of trust coming in for a paticular person and number of trust going a particular person person is 
 # trusting how many people
 
 ## the rule is whenver a person is trusting someone, we increase their value by one in the "in array"
 ## also when a number is been trusted we increase the value by 1
 
 ## let's check if out (trusted) is equal to number of people -1 and they're not trusting anyone
 ### example:
 ## trust = [[[1,3], [1,4], [2,3], [2,4], [4,3]]
 #            0,     1,      2,    3,      4
 
 # in =    [0,      2,       2,     0,     1]
 
 # out =    [0,   0,        0,      3,     2]
 
 
 
 
 from typing import List


class Solution:
    def findJudge(self, n: int, trust: List[List[int]]) -> int:
        if len(trust) < n - 1:
            return -1

        in_list = [0] * (n + 1)
        out_list = [0] * (n + 1)

        for trusting, trusted in trust:
            in_list[trusted] += 1
            out_list[trusting] += 1
        
        for i in range(1, n + 1):
            if in_list[i] == n - 1 and out_list[i] == 0:
                
                return i
                
        
        return -1


g = Solution()

print(g.findJudge(3, [[1,3],[2,3]]))