Dictionary and counter in Python to find winner of election

16 Jun, 2022
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,  
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.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.Now find value of maximum vote casted for a candidate and get list of candidates mapped on that count value.Sort list of candidates having same number of maximum votes and print first element of sorted list in order to print lexicographically smaller name.
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.
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.
Now find value of maximum vote casted for a candidate and get list of candidates mapped on that count value.
Sort list of candidates having same number of maximum votes and print first element of sorted list in order to print lexicographically smaller name.
 
Python3
# Function to find winner of an election where votes# are represented as candidate namesfrom 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 programif __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.  
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 dictionaryvote_count=Counter(votes) #Find the maximum number of votesmax_votes=max(vote_count.values()) #Search for people having maximum votes and store in a listlst=[i for i in vote_count.keys() if vote_count[i]==max_votes] #Sort the list and print lexicographical smallest nameprint(sorted(lst)[0])
Output:  
john
Time complexity : O(n) Auxiliary Space : O(1) 
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