Added "alphametics" exercise

config.json

@@ -1244,6 +1244,24 @@
           "strings"
         ],
         "difficulty": 4
+      },
+      {
+        "slug": "alphametics",
+        "name": "Alphametics",
+        "uuid": "0c69f8bd-c99a-4cb2-b113-82deaf0915ee",
+        "practices": [
+          "auto",
+          "literals"
+        ],
+        "prerequisites": [
+          "includes",
+          "namespaces",
+          "if-statements",
+          "booleans",
+          "headers",
+          "comparisons"
+        ],
+        "difficulty": 6
       }
     ],
     "foregone": [

exercises/practice/alphametics/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Given an alphametics puzzle, find the correct solution.
+
+[Alphametics][alphametics] is a puzzle where letters in words are replaced with numbers.
+
+For example `SEND + MORE = MONEY`:
+
+```text
+  S E N D
+  M O R E +
+-----------
+M O N E Y
+```
+
+Replacing these with valid numbers gives:
+
+```text
+  9 5 6 7
+  1 0 8 5 +
+-----------
+1 0 6 5 2
+```
+
+This is correct because every letter is replaced by a different number and the words, translated into numbers, then make a valid sum.
+
+Each letter must represent a different digit, and the leading digit of a multi-digit number must not be zero.
+
+[alphametics]: https://en.wikipedia.org/wiki/Alphametics

exercises/practice/alphametics/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "marcelweikum"
+  ],
+  "files": {
+    "solution": [
+      "alphametics.cpp",
+      "alphametics.h"
+    ],
+    "test": [
+      "alphametics_test.cpp"
+    ],
+    "example": [
+      ".meta/example.cpp",
+      ".meta/example.h"
+    ]
+  },
+  "blurb": "Given an alphametics puzzle, find the correct solution."
+}

exercises/practice/alphametics/.meta/example.cpp

@@ -0,0 +1,97 @@
+#include <algorithm>
+#include <functional>
+#include <map>
+#include <optional>
+#include <sstream>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+#include "alphametics.h"
+
+namespace alphametics {
+
+std::optional<std::map<char, int>> solve(const std::string& puzzle) {
+    auto sep = puzzle.find("==");
+    if (sep == std::string::npos) return std::nullopt;
+    std::string left = puzzle.substr(0, sep);
+    std::string right = puzzle.substr(sep + 2);
+
+    auto trim = [&](std::string& s) {
+        auto b = s.find_first_not_of(' ');
+        auto e = s.find_last_not_of(' ');
+        s = (b == std::string::npos) ? std::string() : s.substr(b, e - b + 1);
+    };
+    trim(left);
+    trim(right);
+
+    std::vector<std::string> addends;
+    std::istringstream iss(left);
+    for (std::string part; std::getline(iss, part, '+');) {
+        trim(part);
+        addends.push_back(part);
+    }
+    trim(right);
+    std::string result = right;
+
+    std::vector<char> letters;
+    std::unordered_set<char> seen, leading;
+    auto collect = [&](const std::string& w) {
+        if (w.size() > 1) leading.insert(w.front());
+        for (char c : w) {
+            if (seen.insert(c).second) letters.push_back(c);
+        }
+    };
+    for (auto& w : addends) collect(w);
+    collect(result);
+    if (letters.size() > 10) return std::nullopt;
+
+    int n = letters.size();
+    std::map<char, int> idx;
+    for (int i = 0; i < n; ++i) idx[letters[i]] = i;
+    std::vector<long long> weight(n, 0);
+
+    for (auto& w : addends) {
+        long long mult = 1;
+        for (int i = (int)w.size() - 1; i >= 0; --i) {
+            weight[idx[w[i]]] += mult;
+            mult *= 10;
+        }
+    }
+    {
+        long long mult = 1;
+        for (int i = (int)result.size() - 1; i >= 0; --i) {
+            weight[idx[result[i]]] -= mult;
+            mult *= 10;
+        }
+    }
+
+    std::vector<bool> used(10, false);
+    std::map<char, int> assign;
+    bool found = false;
+    std::map<char, int> solution;
+    std::function<void(int, long long)> dfs = [&](int pos, long long sum) {
+        if (found) return;
+        if (pos == n) {
+            if (sum == 0) {
+                found = true;
+                solution = assign;
+            }
+            return;
+        }
+        char c = letters[pos];
+        for (int d = 0; d < 10 && !found; ++d) {
+            if (used[d] || (d == 0 && leading.count(c))) continue;
+            used[d] = true;
+            assign[c] = d;
+            dfs(pos + 1, sum + weight[pos] * d);
+            used[d] = false;
+        }
+    };
+
+    dfs(0, 0);
+    if (found) return solution;
+    return std::nullopt;
+}
+
+}  // namespace alphametics

exercises/practice/alphametics/.meta/example.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <map>
+#include <optional>
+#include <string>
+
+namespace alphametics {
+
+std::optional<std::map<char, int>> solve(const std::string& puzzle);
+
+}  // namespace alphametics

exercises/practice/alphametics/.meta/tests.toml

@@ -0,0 +1,40 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[e0c08b07-9028-4d5f-91e1-d178fead8e1a]
+description = "puzzle with three letters"
+
+[a504ee41-cb92-4ec2-9f11-c37e95ab3f25]
+description = "solution must have unique value for each letter"
+
+[4e3b81d2-be7b-4c5c-9a80-cd72bc6d465a]
+description = "leading zero solution is invalid"
+
+[8a3e3168-d1ee-4df7-94c7-b9c54845ac3a]
+description = "puzzle with two digits final carry"
+
+[a9630645-15bd-48b6-a61e-d85c4021cc09]
+description = "puzzle with four letters"
+
+[3d905a86-5a52-4e4e-bf80-8951535791bd]
+description = "puzzle with six letters"
+
+[4febca56-e7b7-4789-97b9-530d09ba95f0]
+description = "puzzle with seven letters"
+
+[12125a75-7284-4f9a-a5fa-191471e0d44f]
+description = "puzzle with eight letters"
+
+[fb05955f-38dc-477a-a0b6-5ef78969fffa]
+description = "puzzle with ten letters"
+
+[9a101e81-9216-472b-b458-b513a7adacf7]
+description = "puzzle with ten letters and 199 addends"

exercises/practice/alphametics/CMakeLists.txt

@@ -0,0 +1,67 @@
+# Get the exercise name from the current directory
+get_filename_component(exercise ${CMAKE_CURRENT_SOURCE_DIR} NAME)
+
+# Basic CMake project
+cmake_minimum_required(VERSION 3.5.1)
+
+# Name the project after the exercise
+project(${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 ${file}.cpp)
+else()
+    set(exercise_cpp "")
+endif()
+
+# Use the common Catch library?
+if(EXERCISM_COMMON_CATCH)
+    # For Exercism track development only
+    add_executable(${exercise} ${file}_test.cpp ${exercise_cpp} ${file}.h $<TARGET_OBJECTS:catchlib>)
+elseif(EXERCISM_TEST_SUITE)
+    # The Exercism test suite is being run, the Docker image already
+    # includes a pre-built version of Catch.
+    find_package(Catch2 REQUIRED)
+    add_executable(${exercise} ${file}_test.cpp ${exercise_cpp} ${file}.h)
+    target_link_libraries(${exercise} PRIVATE Catch2::Catch2WithMain)
+    # When Catch is installed system wide we need to include a different
+    # header, we need this define to use the correct one.
+    target_compile_definitions(${exercise} PRIVATE EXERCISM_TEST_SUITE)
+else()
+    # Build executable from sources and headers
+    add_executable(${exercise} ${file}_test.cpp ${exercise_cpp} ${file}.h test/tests-main.cpp)
+endif()
+
+set_target_properties(${exercise} PROPERTIES
+    CXX_STANDARD 17
+    CXX_STANDARD_REQUIRED OFF
+    CXX_EXTENSIONS OFF
+)
+
+set(CMAKE_BUILD_TYPE Debug)
+
+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
+# Treat warnings as errors
+# Treat type conversion warnings C4244 and C4267 as level 4 warnings, i.e. ignore them in level 3
+if(${MSVC})
+    set_target_properties(${exercise} PROPERTIES
+        COMPILE_DEFINITIONS_DEBUG _SCL_SECURE_NO_WARNINGS
+        COMPILE_FLAGS "/WX /w44244 /w44267")
+endif()
+
+# Run the tests on every build
+add_custom_target(test_${exercise} ALL DEPENDS ${exercise} COMMAND ${exercise})

exercises/practice/alphametics/alphametics.cpp

@@ -0,0 +1,7 @@
+#include "alphametics.h"
+
+namespace alphametics {
+
+// TODO: add your solution here
+
+}  // namespace alphametics

exercises/practice/alphametics/alphametics.h

@@ -0,0 +1,10 @@
+#if !defined(ALPHAMETICS_H)
+#define ALPHAMETICS_H
+
+namespace alphametics {
+
+// TODO: add your solution here
+
+}  // namespace alphametics
+
+#endif  // ALPHAMETICS_H