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Dictionary and counter in Python to find winner of election

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  • Difficulty Level : Easy
  • Last Updated : 27 Jul, 2022
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Given an array of names of candidates in an election. A candidate name in the array represents a vote cast to the candidate. Print the name of candidates received Max vote. If there is tie, print a lexicographically smaller name.

Examples: 

Input :  votes[] = {"john", "johnny", "jackie", 
                    "johnny", "john", "jackie", 
                    "jamie", "jamie", "john",
                    "johnny", "jamie", "johnny", 
                    "john"};
Output : John
We have four Candidates with name as 'John', 
'Johnny', 'jamie', 'jackie'. The candidates
John and Johny get maximum votes. Since John
is alphabetically smaller, we print it.

We have existing solution for this problem please refer Find winner of an election where votes are represented as candidate names link. We can solve this problem quickly in python using Dictionary data structure

Method 1: 

Approach is very simple, 

  1. Convert given list of votes into dictionary using Counter(iterator) method. We will have a dictionary having candidate names as Key and their frequency ( counts ) as Value.
  2. Since more than 1 candidate may get same number of votes and in this situation we need to print lexicographically smaller name, so now we will create another dictionary by traversing previously created dictionary, counts of votes will be Key and candidate names will be Value.
  3. Now find value of maximum vote casted for a candidate and get list of candidates mapped on that count value.
  4. Sort list of candidates having same number of maximum votes and print first element of sorted list in order to print lexicographically smaller name.

Implementation:

Python3




# Function to find winner of an election where votes
# are represented as candidate names
from collections import Counter
 
def winner(input):
 
    # convert list of candidates into dictionary
    # output will be likes candidates = {'A':2, 'B':4}
    votes = Counter(input)
     
    # create another dictionary and it's key will
    # be count of votes values will be name of
    # candidates
    dict = {}
 
    for value in votes.values():
 
        # initialize empty list to each key to
        # insert candidate names having same
        # number of votes
        dict[value] = []
 
    for (key,value) in votes.items():
        dict[value].append(key)
 
    # sort keys in descending order to get maximum
    # value of votes
    maxVote = sorted(dict.keys(),reverse=True)[0]
 
    # check if more than 1 candidates have same
    # number of votes. If yes, then sort the list
    # first and print first element
    if len(dict[maxVote])>1:
        print (sorted(dict[maxVote])[0])
    else:
        print (dict[maxVote][0])
 
# Driver program
if __name__ == "__main__":
    input =['john','johnny','jackie','johnny',
            'john','jackie','jamie','jamie',
            'john','johnny','jamie','johnny',
            'john']
    winner(input)

Output

john

Time complexity : O(nlogn) 
Auxiliary Space : O(n)

Method 2: 

This is a shorter method.

  1. Count the number of votes for each person and stores in a dictionary. 
  2. Find the maximum number of votes. 
  3. Find corresponding person(s) having votes equal to maximum votes. 
  4. As we want output according to lexicographical order, so sort the list and print first element. 

Implementation:

Python3




from collections import Counter
 
votes =['john','johnny','jackie','johnny','john','jackie',
    'jamie','jamie','john','johnny','jamie','johnny','john']
 
#Count the votes for persons and stores in the dictionary
vote_count=Counter(votes)
 
#Find the maximum number of votes
max_votes=max(vote_count.values())
 
#Search for people having maximum votes and store in a list
lst=[i for i in vote_count.keys() if vote_count[i]==max_votes]
 
#Sort the list and print lexicographical smallest name
print(sorted(lst)[0])

Output

john

Time complexity : O(n) 
Auxiliary Space : O(1)


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