Python – Find the First Non-Repeating Character in a String 🚀 #PythonDSA #CodingInterview

Finding the first non-repeating character in a string is a common problem in coding interviews. Here, we explore two methods to efficiently solve this problem.

🔍 Understanding the Logic:

Method 1 – Using a Dictionary (Long Way)

1️⃣ Create an empty dictionary (char_count) to store character frequencies.

2️⃣ Loop through the string and count occurrences of each character.

3️⃣ Loop again and return the first character with count 1.

4️⃣ If no unique character is found, return None.

🔹 Time Complexity: O(N)

🔹 Space Complexity: O(N)

Method 2 – One-Liner Using collections.Counter

from collections import Counter
print(next((char for char, count in Counter(s).items() if count == 1), None))

✅ Cleaner

✅ Faster

✅ More Pythonic

📌 Here’s how it works:

Counter(s).items() creates a dictionary of character counts.
next((char for char, count in ...) finds the first character with count 1.
If no unique character exists, None is returned.

🔹 Time Complexity: O(N)

🔹 Space Complexity: O(N)

🚀 Why Is This Important?

✅ Common in coding interviews – Asked in Google, Amazon, and Facebook interviews.

✅ Useful in real-world applications – Helps in data parsing, spam detection, and text processing.

✅ Enhances Python skills – Learn to use dictionaries and collections.Counter effectively.

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