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In this semester, I listened the course mit 6.006 in youtube channel. Duirng the course, the professor used different notations to represents time complexity of an algorithm. I learned Big O O(n) notation before, but for Big theta θ(n) and reccurence relations T(n), I never heard them before. Today, I hope I can finally figure them out. What T(n) represents the actual running time of an algorithm O(n) represents the asymptotic upper bound of the running time of an algorithm θ(n) represents the running time when asymptotic upper bound and lower bound of an algorithm ares the same. ...

This week, I browsed many old machines at ebay to use for my first attempt at setting up a homelab. Initially, I planned to build a machine myself during the summer holiday, but in today I found a great performance and a high cost-effective machine that changed my mind. Overview The machine model is HP-Elitedesk-800-G4-SFF. Compared to its previous generation, the chipset supports 8th and 9th generation of intel core cpu, which offers a significant improvement(6c6t) compare with 6th/7th core cpu(4c4t). Furthermore it provides NVme express in this generation. With these components, I can build a highly cost-effective homelab. The total cost is £150. ...

This semester, I learned OOP from Inf1B, which using java as the official teaching language. What fascinates me the most is why Java has the JVM. I learned Python, C++, js and Haskell before, but all of them doesn’t have a jargon for virtual machine. And then I went to wikipeidia to find out why. In 1995, Sun Microsystems introduced Java and the JVM to the world with an ambitious dream: “Write Once, Run Anywhere.” This WORA philosophy became a reality through the JVM, enabling Java applications to run on any operating system with a compatible JVM. Before talking about the archivements and limitations, Let’s have a look about how JVM works. ...