Python – Least Frequent Character in String

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 string
test_str = "GeeksforGeeks"

# printing original string
print ("The original string is : " + test_str)

# using naive method to get
# Least Frequent Character in String
all_freq = {}
for i in test_str:
 if i in all_freq:
  all_freq[i] += 1
 else:
  all_freq[i] = 1
res = min(all_freq, key = all_freq.get)

# printing result
print ("The minimum of all characters in GeeksforGeeks is : " + str(res))

Output : 

The original string is : GeeksforGeeks
The minimum of all characters in GeeksforGeeks is : f

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 string
test_str = "GeeksforGeeks"

# printing original string
print ("The original string is : " + test_str)

# using collections.Counter() + min() to get
# Least Frequent Character in String
res = Counter(test_str)
res = min(res, key = res.get)

# printing result
print ("The minimum of all characters in GeeksforGeeks is : " + str(res))

Output : 

The original string is : GeeksforGeeks
The minimum of all characters in GeeksforGeeks is : f

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Auxiliary Space: O(n)