This article gives us the methods to find the frequency of minimum occurring character in a python string. This is quite important utility nowadays and knowledge of it is always useful. Let’s discuss certain ways in which this task can be performed.
Method 1 : Naive method + min()
In this method, we simply iterate through the string and form a key in a dictionary of newly occurred element or if element is already occurred, we increase its value by 1. We find minimum occurring character by using min() on values.
Python3
# Python 3 code to demonstrate# Least Frequent Character in String# naive method# initializing stringtest_str = "Lazyroar"# printing original stringprint ("The original string is : " + test_str)# using naive method to get# Least Frequent Character in Stringall_freq = {}for i in test_str: if i in all_freq: all_freq[i] += 1 else: all_freq[i] = 1res = min(all_freq, key = all_freq.get)# printing resultprint ("The minimum of all characters in Lazyroar is : " + str(res)) |
The original string is : Lazyroar The minimum of all characters in Lazyroar is : f
Time Complexity: O(n)
Auxiliary Space: O(n), where n is number of characters in string.
Method 2 : Using collections.Counter() + min()
The most suggested method that could be used to find all occurrences is this method, this actually gets all element frequency and could also be used to print single element frequency if required. We find minimum occurring character by using min() on values.
Python3
# Python 3 code to demonstrate# Least Frequent Character in String# collections.Counter() + min()from collections import Counter# initializing stringtest_str = "Lazyroar"# printing original stringprint ("The original string is : " + test_str)# using collections.Counter() + min() to get# Least Frequent Character in Stringres = Counter(test_str)res = min(res, key = res.get)# printing resultprint ("The minimum of all characters in Lazyroar is : " + str(res)) |
The original string is : Lazyroar The minimum of all characters in Lazyroar is : f
The time complexity of this code is O(nlogn) due to the sorting operation done by the min() function.
The auxiliary space used by this code is O(n) because the Counter() function creates a dictionary that stores the count of each character in the string, which can have a maximum of n distinct characters in it.
Method 3: Using defaultdict and list comprehension
In this Method, it finds the least frequent character in a given string by counting the frequency of each character using a defaultdict. It then finds the minimum frequency count and returns the least frequent character(s) by filtering the dictionary keys with the minimum frequency count. The resulting characters are then sorted and the first character is returned.
Python3
from collections import defaultdictdef least_frequent_char(string): freq = defaultdict(int) for char in string: freq[char] += 1 min_freq = min(freq.values()) least_frequent_chars = [char for char in freq if freq[char] == min_freq] return ''.join(sorted(least_frequent_chars))[0]# Example usagetest_str = "GeeksorfGeeks"least_frequent = least_frequent_char(test_str)print(f"The least frequent character in '{test_str}' is: {least_frequent}") |
The least frequent character in 'GeeksorfGeeks' is: f
Time complexity: O(n)
Auxiliary space: O(n)
Method 4: Using numpy:
Algorithm :
- Create an empty dictionary freq.
- For each unique character in the input string string, count the number of times it appears in the string and add it to the dictionary freq with the character as the key and the count as the value.
- Find the minimum value in the dictionary freq using np.argmin.
- Return the corresponding key (character) with the minimum value.
Python3
import numpy as npdef least_frequent_char(string): freq = {char: string.count(char) for char in set(string)} return list(freq.keys())[np.argmin(list(freq.values()))]# Example usageinput_string = "Lazyroar"min_char = least_frequent_char(input_string)print("The original string is:", input_string)print("The minimum of all characters in", input_string, "is:", min_char)#This code is contributed by Jyothi Pinjala. |
Output:
The original string is: Lazyroar
The minimum of all characters in Lazyroar is: f
The time complexity :O(n), where n is the length of the input string. This is because we need to loop through the string once to count the frequency of each character.
The space complexity: O(n), since we create a dictionary freq with at most n key-value pairs.has context menu
Approach: Using Dictionary
Steps:
- Create an empty dictionary to store the frequency of each character in the string.
- Traverse through the given string and update the count of each character in the dictionary.
- Find the minimum value in the dictionary.
- Traverse the dictionary and return the key whose value matches the minimum value.
Python3
# Python program for the above approach# Function to find the least frequent charactersdef least_frequent_char(input_str): freq_dict = {} for char in input_str: freq_dict[char] = freq_dict.get(char, 0) + 1 min_value = min(freq_dict.values()) least_frequent_char = '' # Traversing the dictionary for key, value in freq_dict.items(): if value == min_value: least_frequent_char = key break return least_frequent_char# Driver Codeinput_str = "neveropen"print(least_frequent_char(input_str)) |
f
The time complexity: O(nlogn).
Auxiliary Space: O(n).
