Add build automation tool problem + some cleanup

assignments/[2] build-automation-tool.md

@@ -0,0 +1,83 @@
+## Introduction
+
+When working on large projects, the process of building and testing code might be fairly complex and involve making assumptions about the environment, running multiple commands in a specific sequence, etc. In order to ensure consistency in the process used by different developers, all of this build/test logic is expressed in "build configuration files" (one of many names for this concept), and then triggered by humans when needed during development.
+
+Another benefit of a "build automation tool" is that it can be triggered by machines. In case of small projects, a pre-commit-hook could be configured to run all the tests, while for larger projects (where this would take too long) we could have a separate set of machines responsible for periodically building and testing everything.
+
+Examples = [Make](http://matt.might.net/articles/intro-to-make/), [Buck](https://buck.build/), [NPM](https://docs.npmjs.com/misc/scripts).
+
+## Part 1
+
+You are going to create your own build automation tool.
+What follows is a description of how it will work.
+
+Consider a project with the following file structure:
+```
+algorithms/
+    build.json
+    sort_bubble.cpp
+    sort_merge.cpp
+    sort_quick.cpp
+build.json
+test.cpp
+```
+The `test.cpp` files imports the 3 sorting algorithms and then verifies their correctness. It only contains the declarations of the sorting methods, not the definitions. It does not #include them, so we need to manually link the object files.
+```
+> cat algorithms/build.json
+[
+  {
+    "name": "clean",
+    "command": "rm -f *.o"
+  },
+  {
+    "name": "sort_bubble",
+    "files": ["sort_bubble.cpp"],
+    "command": "g++ -c sort_bubble.cpp"
+  },
+  {
+    "name": "sort_merge",
+    "files": ["sort_merge.cpp"],
+    "command": "g++ -c sort_merge.cpp"
+  },
+  {
+    "name": "sort_quick",
+    "files": ["sort_quick.cpp"],
+    "command": "g++ -c sort_quick.cpp"
+  }
+]
+
+> cat build.json
+[
+  {
+    "name": "clean",
+    "deps": ["algorithms/clean"],
+    "command": "rm -f test.o && rm -f test.exe"
+  },
+  {
+    "name": "test",
+    "files": ["test.cpp"],
+    "command": "g++ -std=c++11 -c test.cpp"
+  },
+  {
+    "name": "run",
+    "deps": ["test", "algorithms/sort_bubble", "algorithms/sort_merge", "algorithms/sort_quick"],
+    "command": "g++ algorithms/sort_bubble.o algorithms/sort_merge.o algorithms/sort_quick.o test.o -o test.exe && ./test.exe"
+  }
+]
+```
+The build automation tool we want should be able to explore the given directory structure, create the necessary dependency graphs, and be capable of running commands like:
+```
+# alias build="python3 build.py"
+# build <name> (where name matches something in the build.json files)
+
+build clean  # deletes all object/exe files
+build run    # compiles, links and runs the code
+```
+
+## Part 2
+
+Until now, the developer was forced to manually trigger the tests. The next step is to do it automatically, whenever any source file is modified ([example](https://webpack.js.org/configuration/watch/)).
+```
+build run --watch
+```
+If the `algorithms/sort_merge.cpp` files was updated by a text editor, your tool should detect this (without using external libraries like [this one](https://github.com/emcrisostomo/fswatch)), recompile only `algorithms/sort_merge.o` and `test.o` (because the other object files will not change), link everything together and finally run the test.

assignments/[3] web-systems-architecture.md

@@ -14,4 +14,4 @@
 - Create a basic website that allows you to manage a to-do list.
 - The user should be able to create an account. The username, password and other information should be stored in a MySQL database.
 - The user should be able to login, and logout. The current login status should be stored in a cookie. The server validates the cookie by checking it against information stored in Memcache.
-- While logged in, the user can items to the to-do list. These items are also stored in the database.
+- While logged in, the user can add items to the to-do list. These items are also stored in the database.