[Python Code] First Repeated Character in String and Count

Problem statement:

Write a Python program to find the first repeated character in a given string and also print the number of times it has occurred.

This coding question was asked in the CGI interview for a Senior Backend developer.

Python program

Prerequisites:

• Python function
• Python if-else block
• Dictionary in Python

Code:

def first_repeated_count(sample):
    desired_ch=""
    char_count={}
    for ch in sample:
      if not desired_ch:
          if ch not in char_count:
              char_count[ch] = 1
          else:
              char_count[ch] += 1
              desired_ch = ch
      else:
          if ch == desired_ch:
              char_count[ch] += 1
    
    return (desired_ch, char_count[desired_ch]) if desired_ch else (None, 0)


repeated_ch, count = first_repeated_count("designsystem") 
  
print(f"The first repeated character is '{repeated_ch}' and it occurred {count} times.")

def first_repeated_count(sample):

    desired_ch=""

    char_count={}

    for ch in sample:

      if not desired_ch:

          if ch not in char_count:

              char_count[ch] = 1

          else:

              char_count[ch] += 1

              desired_ch = ch

      else:

          if ch == desired_ch:

              char_count[ch] += 1

    return (desired_ch, char_count[desired_ch]) if desired_ch else (None, 0)

repeated_ch, count = first_repeated_count("designsystem") 

print(f"The first repeated character is '{repeated_ch}' and it occurred {count} times.")

Output:

The first repeated character is 's' and it occurred 3 times.

The first repeated character here is ‘s’ which occurred three times.

Explanation

• We are initializing the designed character desired_ch as empty.
• As soon as we find the first occurrence of a repeated character, assign that character to the designed character desired_ch.
• dictionary char_count saves the number of occurrences for each character.
• As soon as we find the desired character, we just count the occurrence of the desired character and update it in the chart_count dictionary. And ignoring all other characters.

Complexity:

We are using Python for-loop to traverse each character once, the complexity of this algorithm is O(n).

Regarding the Python program to find the first repeated character, if you have any doubts or have a question, please write me in the comment. Good luck and happy coding!

Aniruddha Chaudhari

I am a Python enthusiast who loves Linux and Vim. I hold a Master of Computer Science degree from NIT Trichy and have 10 years of experience in the IT industry, focusing on the Software Development Lifecycle from Requirements Gathering, Design, Development to Deployment. I have worked at IBM, Ericsson, and NetApp, and I share my knowledge on CSEstack.org.