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Given a string solely consisting of lowercase ASCII letters, write an efficient implementation that returns the first repeated letter.
Looping through the characters looks like a good idea. But what then?
The problem may look less intimidating if you notice there are only 26 possible letters.
It only takes one bit per letter to remember all the letters seen so far.
Then, calculate the single-bit mask representing the current letter.
If it was seen, the success is complete. Otherwise, we must seek further. Mark this letter as seen and keep going.
If the iteration is complete, the result is negative. There you have it, as I promised - an interview question completed in under 60 seconds.
Now follow the link to the video on my channel and learn more tips about programming in C#.

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👨 About Me 👨
Hi, I’m Zoran, I have more than 20 years of experience as a software developer, architect, team lead, and more. I have been programming in C# since its inception in the early 2000s. Since 2017 I have started publishing professional video courses at Pluralsight and Udemy and by this point, there are over 100 hours of the highest-quality videos you can watch on those platforms. On my YouTube channel, you can find shorter video forms focused on clarifying practical issues in coding, design, and architecture of .NET applications.❤️
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