Notizen und Beispiele 7.12.2023

20231207/bogosort-1.c

+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+int is_sorted (char **name)
+{
+  for (int i = 1; name[i]; i++)
+    if (compare (name, i - 1, i) > 0)
+      return 0;
+  return 1;
+}
+
+void mix (char **name)
+{
+  int n = 0;
+  while (name[n])
+    n++;
+  for (int i = 0; i < n; i++)
+    {
+      int j = rand () % (n - i);
+      char *temp = name[i];
+      name[i] = name[j];
+      name[j] = temp;
+    }
+}
+
+void sort (char **name)
+{
+  while (!is_sorted (name))
+    mix (name);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bogosort-2.c

+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+int is_sorted (char **name)
+{
+  for (int i = 1; name[i]; i++)
+    if (compare (name, i - 1, i) > 0)
+      return 0;
+  return 1;
+}
+
+void mix (char **name)
+{
+  int n = 0;
+  while (name[n])
+    n++;
+  for (int i = 0; i < n; i++)
+    {
+      int j = rand () % (n - i);
+      char *temp = name[i];
+      name[i] = name[j];
+      name[j] = temp;
+    }
+}
+
+void sort (char **name)
+{
+  while (!is_sorted (name))
+    mix (name);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bsort-1.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  for (int i = 1; name[i]; i++)
+    if (compare (name, i - 1, i) > 0)
+      {
+        char *temp = name[i - 1];
+        name[i - 1] = name[i];
+        name[i] = temp;
+      }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bsort-2.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0)
+    {
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted--;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bsort-3.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int done = 0;
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0 && !done)
+    {
+      done = 1;
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            done = 0;
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted--;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bsort-3a.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int done = 0;
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0 && !done)
+    {
+      done = 1;
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            done = 0;
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted--;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Anna", "Berta", "Box", "Dieter", "Fritz", "Hans", "Heinrich", "Hugo",
+                   "Lisa", "Maria", "Otto", "Peter", "Siegfried", "Thomas", "Ulrich",
+                   "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bsort-3b.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int done = 0;
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0 && !done)
+    {
+      done = 1;
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            done = 0;
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted--;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Zacharias", "Ulrich", "Thomas", "Siegfried", "Peter", "Otto", "Maria",
+                   "Lisa", "Hugo", "Heinrich", "Hans", "Fritz", "Dieter", "Box", "Berta",
+                   "Anna", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/bsort-4.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, int left, int right)
+{
+  int result = strcmp (name[left], name[right]);
+  comparisons++;
+  display (name, left, right);
+  usleep (200000);
+  return result;
+}
+
+void sort (char **name)
+{
+  int sorted = 0;
+  while (name[sorted])
+    sorted++;
+  while (sorted > 0)
+    {
+      int new_sorted = 0;
+      for (int i = 1; i < sorted; i++)
+        if (compare (name, i - 1, i) > 0)
+          {
+            new_sorted = i;
+            char *temp = name[i - 1];
+            name[i - 1] = name[i];
+            name[i] = temp;
+          }
+      sorted = new_sorted;
+    }
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, -1, -1);
+  return 0;
+}

20231207/hanoi-32.c

+#include <stdio.h>
+#include <error.h>
+
+#define DISKS 32
+
+int n[3], tower[3][DISKS];
+
+void display (void)
+{
+  printf ("\n");
+  for (int i = 0; i < 3; i++)
+    {
+      printf ("tower %d:", i);
+      for (int j = 0; j < n[i]; j++)
+        printf (" %d", tower[i][j]);
+      printf ("\n");
+    }
+}
+
+void move (int from, int to, int disks)
+{
+  if (disks == 1)
+    {
+      if (n[from] <= 0)
+        error (1, 0, "trying to move disk from empty tower");
+      if (n[to] > 0 && tower[to][n[to] - 1] < tower[from][n[from] - 1])
+        error (1, 0, "trying to move larger disk on smaller one");
+      tower[to][n[to]] = tower[from][n[from] - 1];
+      n[to]++;
+      n[from]--;
+      static int counter = 1;
+      if (counter++ >= 100000000)
+        {
+          display ();
+          counter = 1;
+        }
+    }
+  else
+    {
+      int help = 0 + 1 + 2 - from - to;
+      move (from, help, disks - 1);
+      move (from, to, 1);
+      move (help, to, disks - 1);
+    }
+}
+
+int main (void)
+{
+  n[0] = DISKS;
+  for (int i = 0; i < DISKS; i++)
+    tower[0][i] = DISKS - i;
+  n[1] = 0;
+  n[2] = 0;
+  display ();
+  move (0, 2, DISKS);
+  display ();
+  return 0;
+}

20231207/hp-20231207.tex

@@ -248,41 +248,41 @@
         }
       \end{lstlisting}
     \end{onlyenv}
-%     \begin{onlyenv}<6->
-%       \vspace{-5.0cm}
-%       \hspace*{7.4cm}\begin{minipage}[t]{5cm}
-%         32 Scheiben:
-%         \begin{lstlisting}[gobble=10,style=terminal]
-%           $ ¡time ./hanoi-9b¿
-%           ...
-%           real    0m30,672s
-%           user    0m30,662s
-%           sys     0m0,008s
-%         \end{lstlisting}
-%         \pause[7]
-%         \begin{itemize}
-%           \arrowitem
-%             etwas über 1 Minute\\
-%             für 64 Scheiben
-%         \end{itemize}
-%         \pause
-%         \vspace*{-0.5cm}
-%         \begin{picture}(0,0)
-%           \color{red}
-%           \put(0,0){\makebox(0,0)[bl]{\tikz[line width=1pt]{\draw(0,0)--(4,0.8);}}}
-%           \put(0,0.8){\makebox(0,0)[tl]{\tikz[line width=1pt]{\draw(0,0)--(4,-0.8);}}}
-%         \end{picture}
-% 
-%         Für jede zusätzliche Scheibe\\verdoppelt sich die Rechenzeit!
-%         % 30.672 * 2^32 / 3600 / 24 / 365.25 = 4174.43775518138261464750
-%         \begin{itemize}
-%           \arrowitem
-%             $\frac{30,672\,\text{s}\,\cdot\,2^{32}}{3600\,\cdot\,24\,\cdot\,365,25} \approx 4174$
-%             Jahre\\[\smallskipamount]
-%             für 64 Scheiben
-%         \end{itemize}
-%       \end{minipage}
-%     \end{onlyenv}
+     \begin{onlyenv}<6->
+       \vspace{-5.0cm}
+       \hspace*{7.4cm}\begin{minipage}[t]{5cm}
+         32 Scheiben:
+         \begin{lstlisting}[gobble=10,style=terminal]
+           $ ¡time ./hanoi-9b¿
+           ...
+           real    0m30,672s
+           user    0m30,662s
+           sys     0m0,008s
+         \end{lstlisting}
+         \pause[7]
+         \begin{itemize}
+           \arrowitem
+             etwas über 1 Minute\\
+             für 64 Scheiben
+         \end{itemize}
+         \pause
+         \vspace*{-0.5cm}
+         \begin{picture}(0,0)
+           \color{red}
+           \put(0,0){\makebox(0,0)[bl]{\tikz[line width=1pt]{\draw(0,0)--(4,0.8);}}}
+           \put(0,0.8){\makebox(0,0)[tl]{\tikz[line width=1pt]{\draw(0,0)--(4,-0.8);}}}
+         \end{picture}
+ 
+         Für jede zusätzliche Scheibe\\verdoppelt sich die Rechenzeit!
+         % 30.672 * 2^32 / 3600 / 24 / 365.25 = 4174.43775518138261464750
+         \begin{itemize}
+           \arrowitem
+             $\frac{30,672\,\text{s}\,\cdot\,2^{32}}{3600\,\cdot\,24\,\cdot\,365,25} \approx 4174$
+             Jahre\\[\smallskipamount]
+             für 64 Scheiben
+         \end{itemize}
+       \end{minipage}
+     \end{onlyenv}
   \end{onlyenv}
 
 \end{frame}

20231207/hp-20231207.txt

+x ^ 9 = x * x * x * x * x * x * x * x * x         # 8 Multiplikationen
+
+      = ((x^2)^2)^2 * x                           # 4 Multiplikationen
+        `----v----'
+            x^8
+
+
+9 = 1001 binär
+
+    Bits von rechts nach links:
+
+      x        x       1 --> damit multiplizieren
+
+     ^2       x^2      0 --> damit nicht multiplizieren
+    
+     ^2       x^4      0 --> damit nicht multiplizieren
+
+     ^2       x^8      1 --> damit multiplizieren
+   
+--> O(log n) statt O(n)

20231207/names.h

+"Michael",    "Laura",
+"Elias",      "Julia",
+"Luca",       "Anna",
+"Liam",       "Emma",
+"Alexander",  "Lena",
+"Noah",       "Vanessa",
+"Jonas",      "Lea",
+"Marcel",     "Mila",
+"Daniel",     "Lisa",
+"David",      "Lina",
+"Milan",      "Sarah",
+"Julian",     "Alina",
+"Linus",      "Emilia",
+"Thomas",     "Nina",
+"Samuel",     "Elena",
+"Levin",      "Lara",
+"Levi",       "Melanie",
+"Jan",        "Hannah",
+"Lukas",      "Sandra",
+"Tim",        "Leonie",
+"Patrick",    "Sophie",
+"Marvin",     "Mia",
+"Andreas",    "Amelie",
+"Leon",       "Selina",
+"Tobias",     "Luisa",
+"Simon",      "Maria",
+"Valentin",   "Jana",
+"Robin",      "Johanna",
+"Paul",       "Marie",
+"Markus",     "Milena",
+"Benjamin",   "Melina",
+"Stefan",     "Michelle",
+"Felix",      "Emily",
+"Florian",    "Renesmee",
+"Fabian",     "Aylin",
+"Emil",       "Jessica",
+"Aaron",      "Franziska",
+"Manuel",     "Jasmin",
+"Christian",  "Fiona",
+"Dominik",    "Sina",
+"Joshua",     "Jennifer",
+"Moritz",     "Claudia",
+"Sebastian",  "Nicole",
+"Peter",      "Annika",
+"Philipp",    "Sophia",
+"Max",        "Katharina",
+"Johannes",   "Isabella",
+"Finn",       "Nele",
+"Adrian",     "Elisabeth",
+"Martin",     "Pia",

20231207/qsort-1.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}

20231207/qsort-2.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+  if (l < right)
+    quicksort (name, l, right);
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}

20231207/qsort-3.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+  if (r > left)
+    quicksort (name, left, r);
+  if (l < right)
+    quicksort (name, l, right);
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}

20231207/qsort-3a.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+  if (r > left)
+    quicksort (name, left, r);
+  if (l < right)
+    quicksort (name, l, right);
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Anna", "Berta", "Box", "Dieter", "Fritz", "Hans", "Heinrich", "Hugo",
+                   "Lisa", "Maria", "Otto", "Peter", "Siegfried", "Thomas", "Ulrich",
+                   "Zacharias", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}

20231207/qsort-3b.c

+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int comparisons = 0;
+
+void display (char **name, char *pivot, int left, int right)
+{
+  printf ("\e[H\e[J");
+  for (int i = 0; name[i]; i++)
+    {
+      printf ("%s", name[i]);
+      if (name[i] == pivot)
+        printf (" <==");
+      else if (i == left || i == right)
+        printf (" <--");
+      printf ("\n");
+    }
+  printf ("%d\n", comparisons);
+}
+
+int compare (char **name, char *pivot, int left, int right)
+{
+  int result = strcmp (name[left], pivot);
+  comparisons++;
+  display (name, pivot, left, right);
+  usleep (200000);
+  return result;
+}
+
+void quicksort (char **name, int left, int right)
+{
+  int p = (left + right) / 2;
+  char *pivot = name[p];
+  int l = left;
+  int r = right;
+  while (l < r)
+    {
+      while (l < r && compare (name, pivot, l, r - 1) < 0)
+        l++;
+      while (l < r && compare (name, pivot, r - 1, l) > 0)
+        r--;
+      if (l < r)
+        {
+          char *temp = name[r - 1];
+          name[r - 1] = name[l];
+          name[l] = temp;
+          l++;
+          r--;
+        }
+    }
+  if (r > left)
+    quicksort (name, left, r);
+  if (l < right)
+    quicksort (name, l, right);
+}
+
+void sort (char **name)
+{
+  int r = 0;
+  while (name[r])
+    r++;
+  quicksort (name, 0, r);
+}
+
+int main (void)
+{
+  char *name[] = { "Zacharias", "Ulrich", "Thomas", "Siegfried", "Peter", "Otto", "Maria",
+                   "Lisa", "Hugo", "Heinrich", "Hans", "Fritz", "Dieter", "Box", "Berta",
+                   "Anna", NULL };
+  sort (name);
+  display (name, NULL, -1, -1);
+  return 0;
+}

20231207/sort-0.c

+#include <stdio.h>
+
+int find_first (char **name)
+{
+  return 2;
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  int first = find_first (name);
+  printf ("%s\n", name[first]);
+  return 0;
+}

20231207/sort-1.c

+#include <stdio.h>
+#include <string.h>
+
+int find_first (char **name)
+{
+  int first = 0;
+  for (int i = 1; name[i]; i++)
+    if (strcmp (name[i], name[first]) < 0)
+      first = i;
+  return first;
+}
+
+int main (void)
+{
+  char *name[] = { "Otto", "Lisa", "Anna", "Heinrich", "Siegfried", "Peter",
+                   "Dieter", "Hugo", "Berta", "Maria", "Fritz", "Box", "Hans",
+                   "Thomas", "Ulrich", "Zacharias", NULL };
+  int first = find_first (name);
+  printf ("%s\n", name[first]);
+  return 0;
+}