From 21cb4616f05c480210f80b710f5bd7335675c229 Mon Sep 17 00:00:00 2001
From: Olivia Appleton <olivia.kay.appleton@gmail.com>
Date: Mon, 22 Jul 2024 11:23:58 -0500
Subject: [PATCH] solve p0004 in C++

---
 README.rst              |  2 +-
 cplusplus/p0001.cpp     |  5 ++---
 cplusplus/p0002.cpp     |  5 ++---
 cplusplus/p0004.cpp     | 40 ++++++++++++++++++++++++++++++++++++++++
 cplusplus/test_euler.py |  5 +++--
 docs/index.rst          |  2 +-
 6 files changed, 49 insertions(+), 10 deletions(-)
 create mode 100644 cplusplus/p0004.cpp

diff --git a/README.rst b/README.rst
index 977231ce..b3c93598 100644
--- a/README.rst
+++ b/README.rst
@@ -37,7 +37,7 @@ LivInTheLookingGlass’s Project Euler solutions
 |            | ``msvc``, |br|      |        |                   |
 |            | ``pcc``, ``tcc``    |        |                   |
 +------------+---------------------+--------+-------------------+
-| C++        | C++98+ in |br|      |  2     | |Cpi|             |
+| C++        | C++98+ in |br|      |  3     | |Cpi|             |
 |            | ``gcc``, ``clang``, |        |                   |
 |            | ``msvc``            |        |                   |
 +------------+---------------------+--------+-------------------+
diff --git a/cplusplus/p0001.cpp b/cplusplus/p0001.cpp
index 26724a1f..9fbdeea9 100644
--- a/cplusplus/p0001.cpp
+++ b/cplusplus/p0001.cpp
@@ -14,7 +14,7 @@
  */
 #ifndef EULER_P0001
 #define EULER_P0001
-#include <stdio.h>
+#include <iostream>
 
 unsigned long long p0001() {
     unsigned long long answer = 0;
@@ -32,8 +32,7 @@ unsigned long long p0001() {
 
 #ifndef UNITY_END
 int main(int argc, char const *argv[])  {
-    unsigned long long answer = p0001();
-    printf("%llu\n", answer);
+    std::cout << p0001() << std::endl;
     return 0;
 }
 #endif
diff --git a/cplusplus/p0002.cpp b/cplusplus/p0002.cpp
index 87f2389b..765c0b17 100644
--- a/cplusplus/p0002.cpp
+++ b/cplusplus/p0002.cpp
@@ -16,7 +16,7 @@ four million, find the sum of the even-valued terms.
 
 #ifndef EULER_P0002
 #define EULER_P0002
-#include <stdio.h>
+#include <iostream>
 
 unsigned long long p0002() {
     unsigned long long answer = 0,
@@ -37,8 +37,7 @@ unsigned long long p0002() {
 
 #ifndef UNITY_END
 int main(int argc, char const *argv[])  {
-    unsigned long long answer = p0002();
-    printf("%llu\n", answer);
+    std::cout << p0002() << std::endl;
     return 0;
 }
 #endif
diff --git a/cplusplus/p0004.cpp b/cplusplus/p0004.cpp
new file mode 100644
index 00000000..29e71598
--- /dev/null
+++ b/cplusplus/p0004.cpp
@@ -0,0 +1,40 @@
+/*
+Project Euler Problem 4
+
+This was pretty easy to do, given the C++ stdlib
+
+Problem:
+
+A palindromic number reads the same both ways. The largest palindrome made from
+the product of two 2-digit numbers is 9009 = 91 × 99.
+
+Find the largest palindrome made from the product of two 3-digit numbers.
+*/
+#ifndef EULER_P0004
+#define EULER_P0004
+#include <algorithm>
+#include <iostream>
+
+unsigned int p0004() {
+    unsigned int answer = 0, i, j, prod;
+    for (i = 100; i < 1000; i++)    {
+        for (j = 100; j < 1000; j++)    {
+            prod = i * j;
+            std::string forward = std::to_string(prod);
+            std::string reverse = forward;
+            std::reverse(reverse.begin(), reverse.end());
+            if (forward == reverse) {
+                answer = std::max(answer, prod);
+            }
+        }
+    }
+    return answer;
+}
+
+#ifndef UNITY_END
+int main(int argc, char const *argv[])  {
+    std::cout << p0004() << std::endl;
+    return 0;
+}
+#endif
+#endif
diff --git a/cplusplus/test_euler.py b/cplusplus/test_euler.py
index 9e84b59e..143f3fda 100644
--- a/cplusplus/test_euler.py
+++ b/cplusplus/test_euler.py
@@ -22,6 +22,7 @@
 answers = {
     1: 233168,
     2: 4613732,
+    4: 906609,
 }
 
 # this is the set of problems where I have the right answer but wrong solution
@@ -133,10 +134,10 @@
 EXE_TEMPLATE = "{}{}p{{:0>4}}.{{}}.{}".format(BUILD_FOLDER, sep, EXE_EXT)
 # include sep in the recipe so that Windows won't complain
 
-GCC_TEMPLATE = "{} {{}} -O2 -lm -Wall -Werror -std={} -march=native -flto -fwhole-program -o {{}}"
+GCC_TEMPLATE = "{} {{}} -O2 -lstdc++ -lm -Wall -Werror -std={} -march=native -flto -fwhole-program -o {{}}"
 if environ.get('COV') == 'true':
     GCC_TEMPLATE += ' -ftest-coverage -fprofile-arcs'
-CLANG_TEMPLATE = "{} {{}} -O2 {} {} -Wall -Werror -std={} {} -o {{}}"
+CLANG_TEMPLATE = "{} {{}} -O2 -lstdc++ {} {} -Wall -Werror -std={} {} -o {{}}"
 
 templates = {}
 for std in STANDARDS:
diff --git a/docs/index.rst b/docs/index.rst
index 02acb6b7..c36f457c 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -110,7 +110,7 @@ This project is divided into several Makefiles, connected by a root Makefile whi
 +-----------+------------+------------+------------+------------+------------+------------+
 |:prob:`3`  |:c-d:`0003` |            |            |            |:py-d:`0003`|:rs-d:`0003`|
 +-----------+------------+------------+------------+------------+------------+------------+
-|:prob:`4`  |:c-d:`0004` |            |:cs-d:`0004`|:js-d:`0004`|:py-d:`0004`|:rs-d:`0004`|
+|:prob:`4`  |:c-d:`0004` |:cp-d:`0004`|:cs-d:`0004`|:js-d:`0004`|:py-d:`0004`|:rs-d:`0004`|
 +-----------+------------+------------+------------+------------+------------+------------+
 |:prob:`5`  |:c-d:`0005` |            |            |            |:py-d:`0005`|:rs-d:`0005`|
 +-----------+------------+------------+------------+------------+------------+------------+