Implement exercise - luhn

CMakeLists.txt

@@ -68,6 +68,7 @@ foreach(exercise
     isogram
     reverse-string
     acronym
+    luhn
 )
     travis_fixup(${exercise} ${alt_exercise_tree})
     add_subdirectory(${alt_exercise_tree}/${exercise})

config.json

@@ -301,7 +301,7 @@
       "topics": [
         "arrays",
         "math"
-       ]
+      ]
     },
     {
       "slug": "crypto-square",
@@ -389,12 +389,12 @@
       "unlocked_by": null,
       "difficulty": 4,
       "topics": [
-        "control_flow_loops",
         "classes",
         "conditionals",
+        "control_flow_loops",
+        "pairs",
         "strings",
-        "variables",
-        "pairs"
+        "variables"
       ]
     },
     {
@@ -495,7 +495,7 @@
         "strings"
       ]
     },
-    { 
+    {
       "slug": "binary-search",
       "uuid": "abdd7aa3-25f6-4d27-a4dc-6bd1ea2f718c",
       "core": false,
@@ -514,7 +514,7 @@
       "core": false,
       "unlocked_by": "gigasecond",
       "difficulty": 10,
-      "topics":[
+      "topics": [
         "algorithms",
         "classes"
       ]
@@ -531,7 +531,17 @@
         "loops",
         "mathematics"
       ]
+    },
+    {
+      "slug": "luhn",
+      "uuid": "885865bc-a197-436f-94bc-b1998d5cc081",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 1,
+      "topics": [
+        "math",
+        "strings"
+      ]
     }
   ]
 }
-

exercises/luhn/CMakeLists.txt

@@ -0,0 +1,47 @@
+# Get the exercise name from the current directory
+get_filename_component(exercise ${CMAKE_CURRENT_SOURCE_DIR} NAME)
+
+# Basic CMake project
+cmake_minimum_required(VERSION 3.1.3)
+
+# Name the project after the exercise
+project(${exercise} CXX)
+
+# Get a source filename from the exercise name by replacing -'s with _'s
+string(REPLACE "-" "_" file ${exercise})
+
+# Implementation could be only a header
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${file}.cpp)
+    set(exercise_cpp ${file}.cpp)
+else()
+    set(exercise_cpp "")
+endif()
+
+# Build executable from sources and headers
+add_executable(${exercise} ${file}_test.cpp ${exercise_cpp} ${file}.h)
+
+set_target_properties(${exercise} PROPERTIES
+    CXX_STANDARD 11
+    CXX_STANDARD_REQUIRED OFF
+    CXX_EXTENSIONS OFF
+)
+
+if("${CMAKE_CXX_COMPILER_ID}" MATCHES "(GNU|Clang)")
+    set_target_properties(${exercise} PROPERTIES
+        COMPILE_FLAGS "-Wall -Wextra -Wpedantic -Werror"
+    )
+endif()
+
+# Configure to run all the tests?
+if(${EXERCISM_RUN_ALL_TESTS})
+    target_compile_definitions(${exercise} PRIVATE EXERCISM_RUN_ALL_TESTS)
+endif()
+
+# Tell MSVC not to warn us about unchecked iterators in debug builds
+if(${MSVC})
+    set_target_properties(${exercise} PROPERTIES
+        COMPILE_DEFINITIONS_DEBUG _SCL_SECURE_NO_WARNINGS)
+endif()
+
+# Run the tests on every build
+add_custom_target(test_${exercise} ALL DEPENDS ${exercise} COMMAND ${exercise})

exercises/luhn/README.md

@@ -0,0 +1,104 @@
+# Luhn
+
+Given a number determine whether or not it is valid per the Luhn formula.
+
+The [Luhn algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) is
+a simple checksum formula used to validate a variety of identification
+numbers, such as credit card numbers and Canadian Social Insurance
+Numbers.
+
+The task is to check if a given string is valid.
+
+Validating a Number
+------
+
+Strings of length 1 or less are not valid. Spaces are allowed in the input,
+but they should be stripped before checking. All other non-digit characters
+are disallowed.
+
+## Example 1: valid credit card number
+
+```text
+4539 1488 0343 6467
+```
+
+The first step of the Luhn algorithm is to double every second digit,
+starting from the right. We will be doubling
+
+```text
+4_3_ 1_8_ 0_4_ 6_6_
+```
+
+If doubling the number results in a number greater than 9 then subtract 9
+from the product. The results of our doubling:
+
+```text
+8569 2478 0383 3437
+```
+
+Then sum all of the digits:
+
+```text
+8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80
+```
+
+If the sum is evenly divisible by 10, then the number is valid. This number is valid!
+
+## Example 2: invalid credit card number
+
+```text
+8273 1232 7352 0569
+```
+
+Double the second digits, starting from the right
+
+```text
+7253 2262 5312 0539
+```
+
+Sum the digits
+
+```text
+7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57
+```
+
+57 is not evenly divisible by 10, so this number is not valid.
+
+## Getting Started
+
+Make sure you have read the [Installing](https://exercism.io/tracks/cpp/installation) and
+[Running the Tests](https://exercism.io/tracks/cpp/tests) pages for C++ on exercism.io.
+This covers the basic information on setting up the development
+environment expected by the exercises.
+
+## Passing the Tests
+
+Get the first test compiling, linking and passing by following the [three
+rules of test-driven development](http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd).
+Create just enough structure by declaring namespaces, functions, classes,
+etc., to satisfy any compiler errors and get the test to fail.  Then write
+just enough code to get the test to pass.  Once you've done that,
+uncomment the next test by moving the following line past the next test.
+
+```C++
+#if defined(EXERCISM_RUN_ALL_TESTS)
+```
+
+This may result in compile errors as new constructs may be invoked that
+you haven't yet declared or defined.  Again, fix the compile errors minimally
+to get a failing test, then change the code minimally to pass the test,
+refactor your implementation for readability and expressiveness and then
+go on to the next test.
+
+Try to use standard C++11 facilities in preference to writing your own
+low-level algorithms or facilities by hand.  [CppReference](http://en.cppreference.com/)
+is a wiki reference to the C++ language and standard library.  If you
+are new to C++, but have programmed in C, beware of
+[C traps and pitfalls](http://www.slideshare.net/LegalizeAdulthood/c-traps-and-pitfalls-for-c-programmers).
+
+## Source
+
+The Luhn Algorithm on Wikipedia [http://en.wikipedia.org/wiki/Luhn_algorithm](http://en.wikipedia.org/wiki/Luhn_algorithm)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/luhn/example.cpp

@@ -0,0 +1,32 @@
+#include "luhn.h"
+
+using namespace std;
+
+namespace luhn {
+bool valid(string const& input_str) {
+    int result = 0;
+    int counter = 0;
+    for (auto c = input_str.rbegin(); c != input_str.rend(); c++) {
+        if (*c == ' ') {
+            continue;
+        } else if (isdigit(*c)) {
+            const int digit = (int)*c - '0';
+            if (counter % 2 == 1) {
+                result = (digit * 2 > 9) ? (result + digit * 2 - 9)
+                                         : (result + digit * 2);
+            } else {
+                result = result + digit;
+            }
+            counter++;
+        } else {
+            return false;
+        }
+    }
+
+    if (counter > 1) {
+        return result % 10 == 0;
+    } else {
+        return false;
+    }
+}
+}  // namespace luhn

exercises/luhn/example.h

@@ -0,0 +1,10 @@
+#if !defined(LUHN_H)
+#define LUHN_H
+
+#include <string>
+
+namespace luhn {
+bool valid(std::string const&);
+}
+
+#endif  // LUHN_H