feat(6-kyu): https://www.codewars.com/kata/how-many-pages-in-a-book

Closes #54

Author: ParanoidUser

docs/README.md

@@ -6,7 +6,7 @@
            title="Views statistics +1 👀">
    </a>
    <a href="https://www.codewars.com">
-      <img src="https://img.shields.io/badge/solved%20kata-1174-red.svg"
+      <img src="https://img.shields.io/badge/solved%20kata-1175-red.svg"
            title="Solved kata 👌">
    </a>
    <a href="https://github.com/ParanoidUser/codewars-handbook">
@@ -91,7 +91,7 @@ repository.
                title="- Complex language features (closures, scopes, monads, etc)&#13;- Complex OOP/Functional concepts&#13;- Basic Design Patterns&#13;- Complex Regular Expressions">6th kyū
             </a>
          </td>
-         <td>359</td>
+         <td>360</td>
       </tr>
       <tr>
          <td>

kata/6-kyu/how-many-pages-in-a-book/README.md

@@ -0,0 +1,15 @@
+# [How many pages in a book?](https://www.codewars.com/kata/how-many-pages-in-a-book "https://www.codewars.com/kata/622de76d28bf330057cd6af8")
+
+Every book has `n` pages with page numbers `1` to `n`. The `summary` is made by adding up the **
+number of digits** of all page numbers.
+
+Task: Given the `summary`, find the number of pages `n` the book has.
+
+### Example
+
+If the input is `summary=25`, then the output must be `n=17`: The numbers 1 to 17 have 25 digits in
+total: `1234567891011121314151617`.
+
+Be aware that you'll get enormous books having up to 100.000 pages.
+
+All inputs will be valid.

kata/6-kyu/how-many-pages-in-a-book/main/HowManyPagesInABook.java

@@ -0,0 +1,8 @@
+interface HowManyPagesInABook {
+  static int amountOfPages(int s) {
+    return s > 38889 ? 9999 + (s - 38889) / 5 :
+           s > 2889 ? 999 + (s - 2889) / 4 :
+           s > 189 ? 99 + (s - 189) / 3 :
+           s > 9 ? 9 + (s - 9) / 2 : s;
+  }
+}

kata/6-kyu/how-many-pages-in-a-book/test/TestHowManyPagesInABook.java

@@ -0,0 +1,16 @@
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class TestHowManyPagesInABook {
+  @Test
+  void sample() {
+    assertEquals(5, HowManyPagesInABook.amountOfPages(5));
+    assertEquals(17, HowManyPagesInABook.amountOfPages(25));
+    assertEquals(97, HowManyPagesInABook.amountOfPages(185));
+    assertEquals(256, HowManyPagesInABook.amountOfPages(660));
+    assertEquals(401, HowManyPagesInABook.amountOfPages(1095));
+    assertEquals(8365, HowManyPagesInABook.amountOfPages(32353));
+    assertEquals(34902, HowManyPagesInABook.amountOfPages(163404));
+  }
+}

kata/6-kyu/index.md

@@ -161,6 +161,7 @@
 - [Hidden "Cubic" numbers](hidden-cubic-numbers)
 - [Highest Scoring Word](highest-scoring-word)
 - [How Many Numbers?](how-many-numbers)
+- [How many pages in a book?](how-many-pages-in-a-book)
 - [How Much?](how-much)
 - [HTML Complementary Color](html-complementary-color)
 - [HTML dynamic color string generation](html-dynamic-color-string-generation)