2 files changed, 56 insertions, 1 deletions

diff --git a/2015/src/day04.cpp b/2015/src/day04.cpp
new file mode 100644
index 0000000..bc24177
--- /dev/null
+++ b/2015/src/day04.cpp
@@ -0,0 +1,52 @@
+// Standard C++
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <string>
+
+// Standard C
+#include <cstring>
+
+// System
+#include <md5.h>
+
+using namespace std;
+
+void
+brute_force(string_view puzzle, size_t length)
+{
+        array<char, MD5_DIGEST_STRING_LENGTH> digest{};
+
+        string input;
+        for ( unsigned long counter = 0;; ++counter ) {
+                input = puzzle;
+                input += to_string(counter);
+                MD5Data(input.data(), input.size(), digest.data());
+
+                if ( memcmp(digest.data(), "00000000000", length) == 0 ) {
+                        cout << digest.data() << ": " << counter << endl;
+                        return;
+                }
+        }
+}
+
+void
+part1(string_view puzzle)
+{
+        brute_force(puzzle, 5);
+}
+
+void
+part2(string_view puzzle)
+{
+        brute_force(puzzle, 6);
+}
+
+int
+main()
+{
+        string puzzle = "yzbqklnj";
+
+        part1(puzzle);
+        part2(puzzle);
+}
diff --git a/makefile b/makefile
index d88478f..0c313e7 100644
--- a/makefile
+++ b/makefile
@@ -12,6 +12,9 @@ all: $(patsubst 2015/src/%.cpp,2015/bin/%,$(wildcard 2015/src/*.cpp)) \
 2015/bin/%: 2015/src/%.cpp | 2015/bin
         c++ $(CPPFLAGS) $^ -o $@
 
+2015/bin/day04: 2015/src/day04.cpp | 2015/bin
+        c++ $(CPPFLAGS) $^ -lmd -o $@
+
 # 2020
 2020/bin/%: 2020/src/%.cpp | 2020/bin
         c++ $(CPPFLAGS) $^ -o $@
@@ -28,6 +31,6 @@ all: $(patsubst 2015/src/%.cpp,2015/bin/%,$(wildcard 2015/src/*.cpp)) \
         c++ $(CPPFLAGS) -Wno-sign-conversion -I/usr/local/include $^ -L/usr/local/lib -lz3 -o $@
 
 clean:
-        rm -rf 2020/bin 2022/bin 2023/bin
+        rm -rf 2015/bin 2020/bin 2022/bin 2023/bin
 
 .PHONY: all clean