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Count the Number of matching characters in a pair of strings
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Count the number of Unique Characters in a String in Python

Last Updated : 20 Feb, 2025
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We are given a string, and our task is to find the number of unique characters in it. For example, if the string is “hello world”, the unique characters are {h, e, l, o, w, r, d}, so the output should be 8.

Using set

Set in Python is an unordered collection of unique elements automatically removing duplicates when created from a string. The number of unique characters in string can be determined by finding length of set using len().

Python 
a = "hello world"  # Convert the string to a set u_ch = set(a)  # Count the number of unique characters u_c = len(u_ch)  print(f"Number of unique characters: {u_c}")

Output
Number of unique characters: 8

Explanation:

  • Code converts the string “hello world” to a set (set(a)) to extract unique characters as sets automatically remove duplicates.
  • It calculates number of unique characters using len(u_ch) and displays count using a formatted string.

Using collections.Counter

collections.Counter counts character frequencies in a string and stores them as key-value pairs. The number of unique characters is length of Counter object representing distinct keys.

Python 
from collections import Counter  a = "hello world" ch = Counter(a) u_c = len(ch)  print(f"Number of unique characters: {u_c}")

Output
Number of unique characters: 8

Explanation:

  • Counter(a) counts the frequency of each character in string “hello world” and stores counts in a dictionary-like structure.
  • Number of unique characters is determined using len(ch) which gives total number of distinct keys (characters) in Counter.

Using a manual loop

A manual loop iterates through each character in string and adds it to a list or set if it is not already present ensuring only unique characters are tracked. The number of unique characters is then determined by counting the length of resulting collection.

Python 
s = "hello world" u_ch = [] for char in s:     # If the character is not already in the list, add it     if char not in u_ch:         u_ch.append(char)  # Calculate the number of unique characters  u_c = len(u_ch) print(f"Number of unique characters: {u_c}")

Output
Number of unique characters: 8

Explanation:

  • Loop iterates through each character in the string and appends it to the u_ch list only if it hasn’t been added before ensuring all characters are unique.
  • Length of u_ch list is calculated using len() representing number of unique characters in string.


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Count the Number of matching characters in a pair of strings

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Article Tags :
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Practice Tags :
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