I got an initial interview at my university in Mexico. In this first interview, they checked mainly if I could speak proper English and what kind of software I had made as university projects. Finally, I gave them my CV.

The next week, I received an email saying that they were going back to my uni in 2 weeks and asked if I was interested in having a second interview. I said yes, and I took the second interview.

In the second interview, they asked how I would sort a packet of cards and how I would find out which number is missing from 1 to 1,000,000 if I should make a program.

Two weeks later, they told me I had passed the interview and they wanted to interview me at Microsoft headquarters.

Once I got there, I had 4 interviews, 1 person each. The first one was an HR lady; the last 3 were software engineers. The questions were difficult for me; they asked me to write code on the whiteboard.

I failed miserably in 1, and with the 2 others, it went so-so.

In the end, they didn't offer me the job.

If you have all the numbers from 1 to 1,000,000, except one of them, how would you find out which number is missing?