Add StachnissLab Modern C++ homework corrections (HW1–HW3)

.gitignore

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+# Build directories
+HW1/build/
+HW2/build/
+HW3/build/
+
+# Compiled binaries
+HW1/bin/
+HW2/bin/
+HW3/bin/
+
+# CMake generated files
+CMakeCache.txt
+CMakeFiles/
+cmake_install.cmake
+Makefile
+CTestTestfile.cmake
+Testing/
+
+# Static / shared libraries
+*.a
+*.so
+*.so.*
+
+# Editor / IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# macOS
+.DS_Store

README.md

@@ -1 +1,122 @@
-# C-_tutorial
+# C++ Tutorial — StachnissLab Homework Corrections
+
+Solutions to all homework assignments of the **Modern C++ for Computer Vision
+and Image Processing** course by Cyrill Stachniss
+([StachnissLab](https://www.ipb.uni-bonn.de/), University of Bonn).
+
+---
+
+## Prerequisites
+
+| Tool | Version |
+|------|---------|
+| C++ compiler | C++11 or later (g++ / clang++) |
+| CMake | ≥ 3.1 |
+
+---
+
+## Repository structure
+
+```
+.
+├── HW1/   # Homework 1 – Basic C++: string tokenisation & word frequency
+├── HW2/   # Homework 2 – Greyscale image class with PGM file I/O
+└── HW3/   # Homework 3 – Colour image class with Strategy-pattern I/O
+```
+
+---
+
+## HW1 – String operations
+
+**Topics covered:** `std::string`, `std::vector`, `std::map`, range-based for
+loops, function design.
+
+**Tasks:**
+- `Tokenize(str, delimiter)` — splits a string into tokens using a delimiter
+  character, skipping empty tokens.
+- `CountWordFrequency(str)` — counts how often each word appears in a string
+  and returns an alphabetically sorted list of `(word, count)` pairs.
+
+### Build & run
+
+```bash
+cd HW1 && mkdir build && cd build
+cmake ..
+make
+./bin/hw1_main
+ctest --output-on-failure
+```
+
+---
+
+## HW2 – Greyscale image class (`igg::Image`)
+
+**Topics covered:** classes, const/non-const overloading, file I/O streams,
+`std::vector`, histogram computation, image scaling.
+
+**Class interface (`igg::Image`):**
+
+| Method | Description |
+|--------|-------------|
+| `Image()` | Default constructor (empty image) |
+| `Image(rows, cols)` | Constructor — creates a zero-filled image |
+| `int rows() const` | Returns number of rows |
+| `int cols() const` | Returns number of columns |
+| `int& at(row, col)` | Pixel setter (returns mutable reference) |
+| `const int& at(row, col) const` | Pixel getter (returns const reference) |
+| `bool FillFromPgm(file)` | Reads an ASCII PGM (P2) file |
+| `void WriteToPgm(file)` | Writes an ASCII PGM (P2) file |
+| `vector<float> ComputeHistogram(bins)` | Computes pixel-count histogram |
+| `void DownScale(scale)` | Sub-samples by keeping every `scale`-th pixel |
+| `void UpScale(scale)` | Repeats each pixel `scale` times in both dimensions |
+
+**Four demo applications** are provided in `src/application{1..4}/`:
+1. Getter/setter demonstration
+2. Read a PGM file, draw a diagonal, write it back
+3. Compute and print a 10-bin histogram
+4. Downscale and upscale a PGM image
+
+### Build & run
+
+```bash
+cd HW2 && mkdir build && cd build
+cmake ..
+make
+ctest --output-on-failure
+```
+
+---
+
+## HW3 – Colour image class with Strategy pattern (`igg::Image`)
+
+**Topics covered:** inheritance, virtual functions, abstract base classes,
+the Strategy design pattern, colour images (RGB), PPM file format.
+
+**Class hierarchy:**
+
+```
+IoStrategy          (abstract base)
+├── DummyIoStrategy (always succeeds write; returns empty on read — for tests)
+└── PpmIoStrategy   (plain PPM P3 format)
+```
+
+**`igg::Image` interface:**
+
+| Method | Description |
+|--------|-------------|
+| `Image(strategy)` | Constructor — binds an I/O strategy |
+| `Image(rows, cols, strategy)` | Constructor — creates a zero-filled image |
+| `int rows() / int cols()` | Dimension accessors |
+| `Pixel& at(row, col)` | Pixel accessor (read/write) |
+| `const Pixel& at(row, col) const` | Pixel accessor (read-only) |
+| `bool ReadFromDisk(file)` | Reads image via the strategy |
+| `void WriteToDisk(file)` | Writes image via the strategy |
+
+### Build & run
+
+```bash
+cd HW3 && mkdir build && cd build
+cmake ..
+make
+ctest --output-on-failure
+```

homework_4/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.14)
+project(homework_4)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# Fetch Catch2 v2
+include(FetchContent)
+FetchContent_Declare(
+  Catch2
+  URL https://github.com/catchorg/Catch2/releases/download/v2.13.9/catch.hpp
+  DOWNLOAD_NO_EXTRACT ON
+)
+FetchContent_GetProperties(Catch2)
+if(NOT catch2_POPULATED)
+  FetchContent_Populate(Catch2)
+  file(COPY ${catch2_SOURCE_DIR}/catch.hpp DESTINATION ${CMAKE_BINARY_DIR}/include/catch2)
+endif()
+
+# Create interface library for ipb_algorithm
+add_library(ipb_algorithm INTERFACE)
+target_include_directories(ipb_algorithm INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/include)
+
+# Include tests
+enable_testing()
+add_subdirectory(tests)

homework_4/build/DartConfiguration.tcl

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+# This file is configured by CMake automatically as DartConfiguration.tcl
+# If you choose not to use CMake, this file may be hand configured, by
+# filling in the required variables.
+
+
+# Configuration directories and files
+SourceDirectory: /home/franck-albert-fonkoua/C++_tutorials/homework_4
+BuildDirectory: /home/franck-albert-fonkoua/C++_tutorials/homework_4/build
+
+# Where to place the cost data store
+CostDataFile: 
+
+# Site is something like machine.domain, i.e. pragmatic.crd
+Site: franck-albert-fonkoua-IdeaPad-Pro-5-14ARP8
+
+# Build name is osname-revision-compiler, i.e. Linux-2.4.2-2smp-c++
+BuildName: Linux-c++
+
+# Subprojects
+LabelsForSubprojects: 
+
+# Submission information
+SubmitURL: http://
+SubmitInactivityTimeout: 
+
+# Dashboard start time
+NightlyStartTime: 00:00:00 EDT
+
+# Commands for the build/test/submit cycle
+ConfigureCommand: "/usr/bin/cmake" "/home/franck-albert-fonkoua/C++_tutorials/homework_4"
+MakeCommand: /usr/bin/cmake --build . --config "${CTEST_CONFIGURATION_TYPE}"
+DefaultCTestConfigurationType: Release
+
+# version control
+UpdateVersionOnly: 
+
+# CVS options
+# Default is "-d -P -A"
+CVSCommand: 
+CVSUpdateOptions: 
+
+# Subversion options
+SVNCommand: 
+SVNOptions: 
+SVNUpdateOptions: 
+
+# Git options
+GITCommand: 
+GITInitSubmodules: 
+GITUpdateOptions: 
+GITUpdateCustom: 
+
+# Perforce options
+P4Command: 
+P4Client: 
+P4Options: 
+P4UpdateOptions: 
+P4UpdateCustom: 
+
+# Generic update command
+UpdateCommand: 
+UpdateOptions: 
+UpdateType: 
+
+# Compiler info
+Compiler: /usr/lib/ccache/c++
+CompilerVersion: 13.3.0
+
+# Dynamic analysis (MemCheck)
+PurifyCommand: 
+ValgrindCommand: 
+ValgrindCommandOptions: 
+DrMemoryCommand: 
+DrMemoryCommandOptions: 
+CudaSanitizerCommand: 
+CudaSanitizerCommandOptions: 
+MemoryCheckType: 
+MemoryCheckSanitizerOptions: 
+MemoryCheckCommand: /usr/bin/valgrind
+MemoryCheckCommandOptions: 
+MemoryCheckSuppressionFile: 
+
+# Coverage
+CoverageCommand: /usr/bin/gcov
+CoverageExtraFlags: -l
+
+# Testing options
+# TimeOut is the amount of time in seconds to wait for processes
+# to complete during testing.  After TimeOut seconds, the
+# process will be summarily terminated.
+# Currently set to 25 minutes
+TimeOut: 1500
+
+# During parallel testing CTest will not start a new test if doing
+# so would cause the system load to exceed this value.
+TestLoad: 
+
+UseLaunchers: 
+CurlOptions: 
+# warning, if you add new options here that have to do with submit,
+# you have to update cmCTestSubmitCommand.cxx
+
+# For CTest submissions that timeout, these options
+# specify behavior for retrying the submission
+CTestSubmitRetryDelay: 5
+CTestSubmitRetryCount: 3