Implement simple mergesort

docker/Dockerfile

@@ -28,4 +28,3 @@ RUN env; if [[ ${UBUNTU_VERSION} == "23.04" || ${UBUNTU_VERSION} == "23.10" ]];
 
 ARG GCC_VERSION="13"
 RUN apt-get -y install gcc-${GCC_VERSION} g++-${GCC_VERSION}
-

task1/CMakeLists.txt

@@ -18,7 +18,9 @@ add_custom_target(task1_7_dataset
         ${CMAKE_CURRENT_SOURCE_DIR}/dataset.dat
         ${CMAKE_CURRENT_BINARY_DIR}/dataset.dat)
 
-add_executable(task1_7 main.cpp)
+add_executable(task1_7 main.cpp
+        mergesort.h)
+
 target_link_libraries(task1_7
         fmt::fmt
         Qt::Core)

task1/main.cpp

@@ -2,7 +2,8 @@
 #include <QCoreApplication>
 #include <QFile>
 #include <vector>
-#include <printf.h>
+
+#include <mergesort.h>
 
 /*
 Create a simple sorting application that uses the mergesort algorithm to sort a
@@ -23,7 +24,7 @@ your predictions and their graphical illustration?
 int main(int argc, char *argv[]) {
     QFile file("dataset.dat");
     if(!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
-        //qDebug() << "Could not open file";
+        fmt::print("Could not open file");
        return 0;
     }
 
@@ -39,5 +40,22 @@ int main(int argc, char *argv[]) {
 
     fmt::print("Read {} values from {}\n", dataset.size(), file.fileName().toStdString());
 
+    algo::mergesort(dataset.begin(), dataset.end(), [](int32_t a, int32_t b) {
+        return (a>b);
+    });
+
+    QFile outfile("dataset-sorted.dat");
+    if(!outfile.open(QIODevice::WriteOnly | QIODevice::Text)) {
+        fmt::print("Error! Could not create output file");
+    }
+
+    for(auto &val : dataset) {
+        outfile.write(fmt::format("{}\n", val).c_str());
+    }
+
+    file.close();
+    outfile.flush();
+    outfile.close();
+
     return 0;
 }

task1/mergesort.h

@@ -0,0 +1,71 @@
+#pragma once
+
+#include <vector>
+#include <algorithm>
+
+namespace algo {
+
+    template<typename Iterator, typename Comparator>
+    void merge(Iterator start, Iterator middle, Iterator end, Comparator cmp, Iterator output_start) {
+        Iterator start_m = start;
+        Iterator start2 = middle + 1;
+
+        //merge from input until one half completes
+        while (start <= middle && start2 <= end) {
+            if (cmp(*start, *start2)) {
+                *output_start = *start;
+                start++;
+            } else {
+                *output_start = *start2;
+                start2++;
+            }
+            output_start++;
+        }
+
+        //try to finish first half
+        while (start <= middle) {
+            *output_start = *start;
+            start++;
+            output_start++;
+        }
+
+        while (start2 <= end) {
+            *output_start = *start2;
+            start2++;
+            output_start++;
+        }
+
+        const auto nit = std::distance(start_m, end);
+        for (auto i = 0; i <= nit; i++, start_m++, output_start++) {
+            *start_m = *output_start;
+        }
+
+    }
+
+    template<typename Container, typename Iterator, typename Comparator>
+    void mergesort_splitup(Container &output_vec, Iterator start, Iterator end, Comparator cmp, Iterator output_start) {
+        Iterator middle = start;
+        Iterator output_started_from = output_start;
+
+        //move middle iterator litterally to the middle
+        std::advance(middle, std::distance(start, end) / 2);
+        //sort the first half within an recursion
+        mergesort_splitup(output_vec, start, middle, cmp, output_start);
+
+        //move output iterator
+        std::advance(output_start, std::distance(start, middle + 1));
+        //sort the second half within a recursion
+        mergesort_splitup(output_vec, middle + 1, end, cmp, output_start);
+
+        //merge everything together starting from the complete beginning
+        merge(start, middle, end, cmp, output_started_from);
+    }
+
+    template<typename Iterator, typename Comparator>
+    void mergesort(Iterator start, Iterator end, Comparator cmp) {
+        using valtype = typename std::iterator_traits<Iterator>::value_type;
+
+        std::vector<valtype> output_vec(std::distance(start, end));
+
+    }
+}