Add palindrome-products exercise

Author: keiravillekode

config.json

@@ -588,6 +588,14 @@
         "prerequisites": [],
         "difficulty": 6
       },
+      {
+        "slug": "palindrome-products",
+        "name": "Palindrome Products",
+        "uuid": "14453347-8ecf-4e0a-88e6-f4632177251c",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 6
+      },
       {
         "slug": "rail-fence-cipher",
         "name": "Rail Fence Cipher",

exercises/practice/palindrome-products/.docs/instructions.md

@@ -0,0 +1,36 @@
+# Instructions
+
+Detect palindrome products in a given range.
+
+A palindromic number is a number that remains the same when its digits are reversed.
+For example, `121` is a palindromic number but `112` is not.
+
+Given a range of numbers, find the largest and smallest palindromes which
+are products of two numbers within that range.
+
+Your solution should return the largest and smallest palindromes, along with the factors of each within the range.
+If the largest or smallest palindrome has more than one pair of factors within the range, then return all the pairs.
+
+## Example 1
+
+Given the range `[1, 9]` (both inclusive)...
+
+And given the list of all possible products within this range:
+`[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 15, 21, 24, 27, 20, 28, 32, 36, 25, 30, 35, 40, 45, 42, 48, 54, 49, 56, 63, 64, 72, 81]`
+
+The palindrome products are all single digit numbers (in this case):
+`[1, 2, 3, 4, 5, 6, 7, 8, 9]`
+
+The smallest palindrome product is `1`.
+Its factors are `(1, 1)`.
+The largest palindrome product is `9`.
+Its factors are `(1, 9)` and `(3, 3)`.
+
+## Example 2
+
+Given the range `[10, 99]` (both inclusive)...
+
+The smallest palindrome product is `121`.
+Its factors are `(11, 11)`.
+The largest palindrome product is `9009`.
+Its factors are `(91, 99)`.

exercises/practice/palindrome-products/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "PalindromeProducts.pas"
+    ],
+    "test": [
+      "TestCases.pas"
+    ],
+    "example": [
+      ".meta/example.pas"
+    ]
+  },
+  "blurb": "Detect palindrome products in a given range.",
+  "source": "Problem 4 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=4"
+}

exercises/practice/palindrome-products/.meta/example.pas

@@ -0,0 +1,92 @@
+unit PalindromeProducts;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+function smallest(const min, max : UInt64) : UInt64;
+function largest(const min, max : UInt64) : UInt64;
+
+implementation
+
+uses SysUtils;
+
+function palindrome(number: UInt64) : Boolean;
+var
+  digit : UInt64;
+  reversed : UInt64;
+begin
+  if (number mod 10) = 0 then
+    begin
+      result := (number = 0);
+      exit;
+    end;
+
+  reversed := 0;
+  while number <> 0 do
+    begin
+      digit := number mod 10;
+      number := number div 10;
+
+      if number = reversed then
+        begin
+          result := true;
+          exit;
+        end;
+
+      reversed := reversed * 10 + digit;
+      if number = reversed then
+        begin
+          result := true;
+          exit;
+        end;
+    end;
+
+  result := false;
+end;
+
+function smallest(const min, max : UInt64) : UInt64;
+var
+  first : UInt64;
+  second : UInt64;
+  product : UInt64;
+begin
+  if min > max then
+    raise ENotImplemented.Create('min must be <= max');
+
+  result := min * max + 1;
+  for first := min to max do
+    for second := first to max do
+      begin
+        product := first * second;
+        if (result > product) and palindrome(product) then
+          result := product;
+      end;
+
+  if result = min * max + 1 then
+    raise ENotImplemented.Create('no solution');
+end;
+
+function largest(const min, max : UInt64) : UInt64;
+var
+  first : UInt64;
+  second : UInt64;
+  product : UInt64;
+begin
+  if min > max then
+    raise ENotImplemented.Create('min must be <= max');
+
+  result := 0;
+  for first := min to max do
+    for second := first to max do
+      begin
+        product := first * second;
+        if (result < product) and palindrome(product) then
+          result := product;
+      end;
+
+  if result = 0 then
+    raise ENotImplemented.Create('no solution');
+end;
+
+end.

exercises/practice/palindrome-products/.meta/tests.toml

@@ -0,0 +1,49 @@
+# 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.
+
+[5cff78fe-cf02-459d-85c2-ce584679f887]
+description = "find the smallest palindrome from single digit factors"
+
+[0853f82c-5fc4-44ae-be38-fadb2cced92d]
+description = "find the largest palindrome from single digit factors"
+
+[66c3b496-bdec-4103-9129-3fcb5a9063e1]
+description = "find the smallest palindrome from double digit factors"
+
+[a10682ae-530a-4e56-b89d-69664feafe53]
+description = "find the largest palindrome from double digit factors"
+
+[cecb5a35-46d1-4666-9719-fa2c3af7499d]
+description = "find the smallest palindrome from triple digit factors"
+
+[edab43e1-c35f-4ea3-8c55-2f31dddd92e5]
+description = "find the largest palindrome from triple digit factors"
+
+[4f802b5a-9d74-4026-a70f-b53ff9234e4e]
+description = "find the smallest palindrome from four digit factors"
+
+[787525e0-a5f9-40f3-8cb2-23b52cf5d0be]
+description = "find the largest palindrome from four digit factors"
+
+[58fb1d63-fddb-4409-ab84-a7a8e58d9ea0]
+description = "empty result for smallest if no palindrome in the range"
+
+[9de9e9da-f1d9-49a5-8bfc-3d322efbdd02]
+description = "empty result for largest if no palindrome in the range"
+
+[12e73aac-d7ee-4877-b8aa-2aa3dcdb9f8a]
+description = "error result for smallest if min is more than max"
+
+[eeeb5bff-3f47-4b1e-892f-05829277bd74]
+description = "error result for largest if min is more than max"
+
+[16481711-26c4-42e0-9180-e2e4e8b29c23]
+description = "smallest product does not use the smallest factor"

exercises/practice/palindrome-products/Makefile

@@ -0,0 +1,15 @@
+SHELL       = /bin/bash
+MAKEFLAGS  += --no-print-directory
+DESTDIR     = build
+EXECUTABLE  = $(DESTDIR)/test
+COMMAND     = fpc -l- -v0 -g -gl -Sa -Cr -Sehnw -Fu./lib test.pas -FE"./$(DESTDIR)"
+
+.ONESHELL:
+
+test:
+	@mkdir -p "./$(DESTDIR)"
+	@cp -r ./lib "./$(DESTDIR)"
+	@$(COMMAND) && ./$(EXECUTABLE) $(test)
+
+clean:
+	@rm -fr "./$(DESTDIR)"

exercises/practice/palindrome-products/PalindromeProducts.pas

@@ -0,0 +1,28 @@
+unit PalindromeProducts;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+function smallest(const min, max : UInt64) : UInt64;
+function largest(const min, max : UInt64) : UInt64;
+
+implementation
+
+uses SysUtils;
+
+function smallest(const min, max : UInt64) : UInt64;
+begin
+
+  raise ENotImplemented.Create('Please implement your solution.'); result := min * max;
+
+end;
+
+function largest(const min, max : UInt64) : UInt64;
+begin
+
+  raise ENotImplemented.Create('Please implement your solution.'); result := min * max;
+
+end;
+
+end.