Python – String with most unique characters

Sometimes, while working with python strings, we can have a problem in which we desire to extract particular list which has most number of unique characters. This kind of problem can have application in competitive programming and web development domain. Lets discuss certain ways in which this task can be performed.

Method #1 : Using max() + dictionary comprehension The combination of above functionalities can be used to perform this task. In this, we firstly collect the frequency of each character using dictionary and then employ max() to compute the string with most unique characters.

Python3

# Python3 code to demonstrate 
# String with most unique characters
# using max() + dictionary comprehension
 
# Initializing list

test_list = ['gfg', 'is', 'best', 'for', 'geeksc']
 
# printing original list

print("The original list is : " + str(test_list))
 
# String with most unique characters
# using max() + dictionary comprehension

temp =  {idx : len(set(idx)) for idx in test_list}

res = max(temp, key = temp.get)
 
# printing result 

print ("The string with most unique characters is : " + str(res))

Output :

The original list is : ['gfg', 'is', 'best', 'for', 'geeksc']
The string with most unique characters is : geeksc

Time Complexity: O(n) where n is the number of elements in the list “test_list”.
Auxiliary Space: O(n) where n is the number of elements in the list “test_list”.

Method #2 : Using max() + key + lambda The combination of above methods can be used to perform this task. In this, we perform this task in similar way as above, just the difference is instead of using comprehension we use lambda function to extend logic to each string for computation.

Python3

# Python3 code to demonstrate 
# String with most unique characters
# using max() + key + lambda
 
# Initializing list

test_list = ['gfg', 'is', 'best', 'for', 'geeksc']
 
# printing original list

print("The original list is : " + str(test_list))
 
# String with most unique characters
# using max() + key + lambda

res = max(test_list, key = lambda sub: len(set(sub)), default = None)
 
# printing result 

print ("The string with most unique characters is : " + str(res))

Output :

The original list is : ['gfg', 'is', 'best', 'for', 'geeksc']
The string with most unique characters is : geeksc

Method#3:Using Counter()+keys()+list() functions

Python3

# Python3 code to demonstrate
# String with most unique characters

from collections import Counter
 
# Initializing list

test_list = ['gfg', 'is', 'best', 'for', 'geeksc']
 
# printing original list

print("The original list is : " + str(test_list))
 
# String with most unique characters

res = []

stringres = ""

for i in test_list:

    freq = Counter(i)

    if(len(freq) >= len(res)):

        res = list(freq.keys())

        stringres = i
# printing result
 
print("The string with most unique characters is : " + str(stringres))

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeksc']
The string with most unique characters is : geeksc

Time Complexity: O(N)

Auxiliary Space: O(N)

Method #4 : Using numpy

Note: Install numpy module using command “pip install numpy”

Python3

# Python3 code to demonstrate
# String with most unique characters
# using max() + dictionary comprehension

# Importing numpy library

import numpy as np
 
# Initializing list

test_list = ['gfg', 'is', 'best', 'for', 'geeksc']

# printing original list

print("The original list is : " + str(test_list))

# String with most unique characters
# using max() + dictionary comprehension

temp =  {idx : len(np.unique(list(idx))) for idx in test_list}

res = max(temp, key = temp.get)

# printing result

print ("The string with most unique characters is : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

Output:

The original list is : [‘gfg’, ‘is’, ‘best’, ‘for’, ‘geeksc’]
The string with most unique characters is : geeksc

Explanation:

In this code, we are importing the numpy library to use np.unique() function.
We initialize a list test_list of strings.
We use a dictionary comprehension to create a dictionary temp with the length of unique characters in each string of test_list as the values and the corresponding strings as keys.
The np.unique() function takes a list as input and returns an array of unique elements of that list.
Then, we use the max() function with temp.get as the key to get the string with the most number of unique characters.
The result is the string with the most number of unique characters.

Time complexity: O(N)
Auxiliary space: O(N)

Method #5 : Using sorted() function and len() function

Convert the list to tuples where each tuple contains: the string and its set of unique characters.
Sort the list of tuples by the length of the set of unique characters in descending order.
Return the first element of the sorted list of tuples, which will be the string with the most unique characters.

Python3

# Python3 code to demonstrate 
# String with most unique characters
 
# Initializing list

test_list= ['gfg', 'is', 'best', 'for', 'geeksc']
 
# printing original list

print("The original list is : " + str(test_list))
 
# creating list of tuples with string and its set of unique characters

list_tuples = [(s, set(s)) for s in test_list]
 
# sorting the list of tuples

sorted_list = sorted(list_tuples, key=lambda x: len(x[1]), reverse=True)
 
# returning the first element

result = sorted_list[0][0]
 
# printing result 

print ("The string with most unique characters is : "+ str(result))

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeksc']
The string with most unique characters is : geeksc

Time complexity: O(N*log(N)) as for sorting the list of strings, and then O(n) for iterating over the sorted list
Auxiliary space: O(N) as we are creating the sorted list of strings .

Method #6: Using for loop and dictionary

Algorithm:

Initialize an empty string variable max_str and a variable max_count to 0.
Iterate over each string s in the list test_list:
a. Initialize an empty dictionary char_dict to store the unique characters of s.
b. Iterate over each character c in s:
i. If c is not already in char_dict, add it with a value of 1.
c. Calculate the length of char_dict and store it in the variable count.
d. If count is greater than max_count, update max_count to count and max_str to s.
Print the value of max_str

Python3

test_list = ['gfg', 'is', 'best', 'for', 'geeksc']
# printing original list

print("The original list is : " + str(test_list))

max_str = ''

max_count = 0

for s in test_list:

    char_dict = {}

    for c in s:

        if c not in char_dict:

            char_dict = 1

    count = len(char_dict)

    if count > max_count:

        max_count = count

        max_str = s

print(f"The string with most unique characters is: {max_str}")
#This code is contributed by Vinay Pinjala.

Output

The original list is : ['gfg', 'is', 'best', 'for', 'geeksc']
The string with most unique characters is: geeksc

The time complexity of this algorithm is O(n*m), where n is the length of the input list test_list and m is the maximum length of a string in test_list.

The outer loop iterates over each string in the list once, and the inner loop iterates over each character of the string once. Therefore, the time complexity is proportional to the number of strings times the maximum length of a string.

The auxiliary space of this algorithm is also O(n*m), because we create a dictionary for each string in the list, with a maximum size of m characters. Therefore, the space required is proportional to the number of strings times the maximum length of a string.

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